A lot of guys will tell you about certain patterns that they swear by and how great that pattern is, but I honestly dont think that the fly matters too much.
I tie a ton of flies that are very simple and very effective. For cohos and SRCs, if it looks like a baitfish, it is a baitfish. A lot of the flies I use are just a little crystal flash, some bucktail, maybe a little blue bucktail on its back and 2 peacock hurls for a dark back. I also really like having eyes on my flies and think that they can make a big difference in how effective a fly is.
One thing that I have found is that epoxy head flies are great because they hold up so well after catching a lot of fish.
I like clousers a lot too. pink/white & chart./white are both good. I also like purple and chartuse clousers. I dont know why they work but they are very effective.
Most of my flies are size 4 but I also tie some 2s and 6s depending on the size of the baitfish that are in the area at the time.