Hmmm... My favorite is stocker trout! J/J ;D
Ok, I'll be serious. I would have to say it is a close call between wiper and crappie. Crappie (slabs) are just too fun and challenging at the same time while wiper are the only fish I know that will give me a work out even when it is smaller than the size limit (15 inches at most Reservoirs).
Since this is a "favorite species" subject and I'm bored out of my mind while sitting here at work, I'll talk about other species I like and why.
Stocker Rainbows: easy to catch, but it aint a sunfish. Yeah!
Walleye: walleye rhymes with eye and FRY!
Brook Trout: camping food (cook em on a stick with salt and pepper and then I eat em with plain steamed rice)
Largemouth Bass: tought me a bunch about soft plastics. I owe it to the Bigmouths
Smallies: the beautiful bronze fish comes next to the wiper when you're talkin pound for pound fighting, though some will disagree
Channel Catfish: the best way to make use of summer insomnia
White Bass: puts up a fight too
Brown Trout: the bigger trout of my life were these