I keep Trout, Perch, Walleye, and Crappie in FW because they're tasty. I release any other fish native to my area. Non-natives I destroy, with the exception of Rainbow and Brown Trout which like I said I eat. In SW I keep Fluke and Tautog.
I usually only wade in saltwater and I keep all fish that are edible and of legal size and bag limit. Anything else I release as careful as possible. Just this week I brought home 3 nice macs and a trout. YUM! Also a porcupine puffer caught in my cast net that is now in my 125g.