When I was looking at Philmont Scout Ranch, Philmont recommends rain jacket and rain pants. Of course, I have those two items. And, of course a few folks used other rain gear (I saw at least one poncho). And I thought I would keep this separate from the umbrella conversation.
I generally use hooded ponchos unless I am in very brushy country. The poncho does double duty as a tarp shelter s well.
I use a very long rain jacket (comes down to the lower thighs) that has an integrated "camel-hump" like pouch that acts as a pack cover. All in one garment. Hooded & pit zips. I love it. It's called "The Packa" made by Cedar Tree.
on the flip side, I would say definitely forget ponchos. I have 2 very nice 'backpacking ponchos' from REI, probably purchased over 20 yrs ago, still have. Got them in red for use with scouts.
But, here's the problem, they won't keep you dry - period. They also suck in any type of breeze, forget wind...and...all the water coming off them just drains onto your pants.
In the context of backpacking, if it's raining, if you put on your rain jacket you're going to get soaked due to sweat.
here's what I preach. If it is NOT COLD and little chance of hypothermia, you're going to get wet, so walk in your 1 set of hiking clothes, change to your 1 set of dry clothes when you get to camp, after you've got water and tent up, or if the sun comes out, walk your wet clothes dry. If not, put back on your wet clothes in the morning and walk them dry. It sucks, but you're not going to carry 4 sets of clothes, including a wet set.
IF it is cool enough that you're getting cold in the rain, put on your rain jacket, but it should be cold/cool enough that you'll strike a balance between the heat you're generating, so you won't be sweating.
Remember, if you put on your jacket, and it's not cool enough, your shirt is going to get soaked anyway and you don't want to overheat.
I've written several articles on this, I call it rain management versus how to stay dry. Others may disagree, but I'm always seeking to learn new techniques myself.
by the way, this applies to goretex jackets and another breathable products.
The trick is only putting on the jacket to stay warm/comfortable and not sweat to death.
Believe me, I've made these mistakes and paid the price. I've tried to warn others about NOT doing this and sometimes it's a hard sell. What happens is, folks will get to camp, walking clothes soaked, from either the rain and/or sweating under the rain jacket, put on the dry set, then in the morning, the 1st set is still wet, but now cold, and a bear to put back on, so they'll hike in the only remaining dry set, now, if that set get wets YOU ARE TOAST.
Just like your sleeping bag, and anything down, 1 dry set of clothes can be your last line of defense against hypothermia. You must have a plan to keep this stuff dry!
sadly this is me learning/re-learning this lesson, the hard way, in the white mountains in New Hampshire, on the AT, put on not only my jacket but rain pants, not only got soaked, but dangerously overheated.