Cherry for salmonand other fish, hands down.
Apple and cherry for fowl with perhaps a little oak, mesquite or hickory. Maybe a little black walnut too.
Mesquite, oak and some hickory for beef.
Hickory and maple for pork. OK, I'll usually throw in some apple and/or cherry.
This was the motivation to build my mini-WSM. I had a bunch of smoking woods, some purchased and some collected locally. I didn't know which to use. Neither did I want to fire up a full (or nearly empty 18.5 WSM) to test wood. I do that in the mini. I build a fire with a single smoking wood and then cook a couple pieces of chicken, a couple hamburger patties, a couple pork streaks, a couple pieces of salmon and tilapia. I cover fowl, beef, fish and pork and with no other seasoning save some peanut oil. Oh, yeah... A couple slices of potato. Then I take notes on what I like and what I don't as well as the appearance. That helps to guide me as to what wood I'll use depending on what I plan to smoke.
It's an experiment well worth doing.