Is a full waterproof coat more important than waterproof trousers for hiking?

I can totally see your point of view as your coming from forestry or generally working outdoors, but this is fairly straight forward from a hiking point of view:

Hiking is walking, meaning work for your legs. I never had cold legs while walking, but the fairly idle arms get cold much faster. Furthermore, open armpits are an easy entry for rain to your core, which is well prevented by coats with arms. Whether or not to use waterproof trousers depends on two factors: The first is the one you already mentioned: Is there a possibility to get dry at the end of the day? Second issue is with conditions: In (near) freezing conditions or any situation, where short term inactivity (no more heating your legs) can already be critical (or simple highly uncomfortable). Why not always use water-proof trousers: Increased sweating, increased cost when trashing them (I kill trousers quickly) and weight.

I have to say when i hiked the PCt, I completed 90% of it in shorts, I did bring wet trousers but never used them. I did however use a rain jacket on many occasions . I found i got too hot in rain pants and found that my shorts quickly dried out. Maybe if its really cold i may of worn them. But even marching through snow shorts were good for me

I say you should always wear the gear that you already own and you are comfortable in instead of following some fashion trend. If you like your setup go for it.

Beyond that I think there are some reasons why people tend to recommend a coat over a vest. First and foremost when you are earning a living outdoors you work more or less in all kinds of weather. When you go outdoors for recreation you try your best to only go when the weather is going to be reasonably good. This is where the no waterproof pants comes in. People will bring a jacket for warmth and a hedge against inclimate weather. Like imasodin said when hiking your arms are more likely to get cold and a jacket keeps the weather out better than a vest. If people think odds are good they will encounter significant moisture then people bring water proof pants. Like I said people mostly want to go hike when they think it isn't going to rain so carrying full rain gear is unnecessary but a good jacket that works for wind, water, and general warmth makes perfect sense.

Another consideration is most hikers don't have quality wool long sleeve shirts because you don't find them in generic outdoors stores like REI where many hikers shop. There's a couple reasons for this but the biggest one in my opinion is hiker/backpacker fashion follows climbing/mountaineering clothing trends. These realms embrace fancy synthetic fibers due to their light weight. I have some Army surplus thick wool pants that are phenomenal for a cold rainy day. Of course they weigh a ton, aren't worn by serious mountaineers anymore for that reason, and as a result aren't being marketed by major brands because who really wants to go for a 10 mile hike in the pouring rain where you can't see the dramatic sweeping views anyway?

To address the poncho bit some people do carry ponchos with them in case it rains. Of course since they aren't planning on going out when it is raining these ponchos are the thin plastic "emergency" ponchos. Ponchos are fabulous for walking around in when it is wet but they also aren't as functional as pants and a jacket for climbing or mountaineering. Of course you aren't going to plan on climbing or mountaineering in the rain but if you do I know I'd rather be reaching over my head in the rain with a jacket than a poncho.

In summary:

• Wear what you have if it is comfortable
• most people plan trips around good weather
• Hiker fashion follows backpacker/climbing/mountaineering fashion where weight savings are prized above almost all else
• Jackets offer a good balance of protection from the wind, cold, and occasional rainfall.
• Vests are rare since jackets are so dominant and as a result the shirts commonly found in stores pair better with jackets than vests.

Intro:

You can get wet from sweat or wet from rain, or a combination. The waterproof breathables depend on the outside surface being not wet. So the outside layer has to shed water. This generally works well in light to moderate rains -- up to about 1 mm/hour, but fails in major downpours. You will get wet where pack straps bear down on your shoulders, and at least damp between your pack and your body. This is one reason I prefer an external frame pack. Less of it presses against you.

Ponchos

The poncho comes in a variety of shapes. One version has a longer back so it can be worn over your pack. I have generally stayed drier in a poncho than in a raincoat, as there is LOTS of ventilation. Some have snaps on the edge you can use to make short sleeves for your arms, or reduce the wind catching on them. Recommended.

A poncho is a pain in the wind, and it tends to catch in brush, or crossing deadfall. The wind issue can be relieved somewhat by making a belt out of elastic waist band material (1" wide plus snap click buckles.) This usually makes the brush problem worse.

Ponchos are ok for walking or standing around, but seem to constantly be in the way if you are working, Try setting 2 foot survey sticks, or doing litter pickup wearing a poncho. Ugh.

I've used ponchos canoeing too. The waist belt is necessary here, as the wind can flip either end over your vision in a hurry. I was uneasy about dumping wearing a poncho, enough so that I removed it and tucked it away when we came to rapids. Wearing your life jacket over your poncho helps a lot. Ponchos for canoeing have a longer front so your lap and thighs are covered.

Raincoats

This is a jacket with a water impermeable layer. The most common is urethane coated nylon. I expect now there are silicone nylon ones. They are perfect at keeping the rain out. And at keeping the sweat in. They are inexpensive, and if you are in a climate where it rains a lot or you are in a situation with a lot of water in the air (sailing...) they are a good solution. You will get wet from sweat condensation, but you will be warm and damp.

Waterproof breathables

Gore tex is in the lead here, but there are several competitors. The waterproof layer in a goretex jacket is a separate layer. Good jackets have a liner layer too to protect the magic (It's a sheet of teflon that's been stretched.) This makes the jacket somewhat heavier, and a 3 layer construction is more expensive.

They aren't fully waterproof due to needle holes to sew. Good ones are seam sealed at critical points -- shoulder seams.

There are various breathable membranes that can be stuck to the fabric. These are much less expensive since the garment is then only single layer construction, but it tends not to work as well as the gore tex ones.

Wet weather clothing in general:

In general the synthetic fabrics work better. They can get wet, but the water isn't absorbed by the fiber itself. Wring it out well, and it's generally just damp, but will now trap enough air that it's reasonable warm, even though you feel like you are making love to a clam.

You have 3 different issues: Insulation, water resistance, wind resistance. Often blocking the wind over a light layer is sufficient. You will use various combinations depending on circumstances.

Fleece is warm, but has very little wind resistance. A wind parka has excellent wind resistance, but little insulation value.

Sometimes I've come up with interesting combinations:

Tracking and lining canoeing: Sunny day: Water boots, running shorts, life jacket and toque (aka watchman's cap, stocking cap, mitten hat) when I start getting chilly. Cloudy day. Add polypro top and bottom.

The poly gets wet, but it's barely damp 20 minutes after you are out of the water.

2 inches of snow the night before. All the brush with leaves full of slush the next morning -- but bright sun and warm. Shorts, no shirt. Got a blast of ice water every couple hundred feet when had to pass between two bushes, but overall was comfortable.

-15 C, bright sun. snowshoeing. Wind pants over poly bottom. Wind parka over skin top. Just blocking the wind was enough.

-40 C, 30-40 kph winds. Winter parka, two fleeces, toque and balaclava, polypro top and bottom, fleece pants, wind pants, felt lined boots 3 sizes to large with 3 pairs wool socks, leather mitts with fleece liners, and thin polypro gloves. (the latter give full dexterity, but your skin doesn't freeze to dog clips.)

At present my preferred system for hiking:

Note: I'm in central Alberta. If it rains here, the temperature drops to about 10 C (50 F) in a hurry. In the mountains you can get snow any month of the year, and even in August hard frosts on a clear night are common.

Tight weave nylon wind pants with full leg zip. This allows you to unzip the cuffs a bit so water drains faster after fording a stream, and allows you to unzip the sides at the top for more ventilation. It also means you can put them on and off without taking off your boots. Do not get the super light weight ones made from rip stop nylon unless you are on groomed trails all the time. Look for material equivalent to what is often used in kids book bags at the light end, to lightweight jean fabric at the heavier end.

A goretex parka. Avoid the lightweight ones. MEC has a line made from heavy nylon canvas as the outer layer. This is certainly proof against spruce twigs and wild rose. Haven't tested it against Devil's club.

Under the parka a minimum of a dry wick t-shirt. More commonly, a light weight polypro top, long sleeve. If it's colder I have a medium weight fleece. Usually my legs are warm enough due to the effort of hiking, but if not, I also have along polypro bottoms. These come out if the temperatures are close to freezing, and I'm walking through rain soaked brush.

If the weather is consistently below freezing, I will wear a wind parka that is not water proof. Most of the breathables don't work well below freezing if they are decent at above freezing temps. The pores in the magic layer plug with ice.

On my head I usually have a toque. I like the cheap acrylic ones that you can get at the dollar store. I usually carry two, one for day time use, and one to sleep in.

All jackets are below-the-butt length. This puts them mid thigh in front. I don't like elastic waists: They impede airflow, and I get wetter. Having a draw string at the waist level can be useful on windy days, but I use it rarely. A loose lower end means that as you move more, the garment flaps more allowing warm humid air to move through the insulation area. This, along with hood on or off, top zip, gives good ventilation.

When hiking in light rain, I often only do up a couple of snaps on the front. This gives me reasonable rain coverage, but leaves good ventilation.

On my feet I usually wear a thin pair of poly pro socks and a pair of thick wool/nylon socks. If there isn't snow on the ground, I wear low cut trail shoes.