I've used just about everything under the sun. Trash bag, poncho, Gortex, etc. The best I have used is Frogg Toggs. There lightweight and no rain gets through them. Gortex is good but if it's warm outside, forget it. You'll be as wet as if you had just left it off. Different kinds of gear for different circumstances.
Bottom line I carry two sets in my boat...Gortex and Frog Togg.
The Hound