I've pretty much always stuck with the X-Men, with occasional side forays (Strikefore:Morturi; New Universe; Sandman -> Lucifer -> Fables)
My favorite hero is pretty hard to pick out - there are a lot with potential that's not (IMO) realized, others that are overused now but weren't ten or fifteen years ago....
I liked the Silvestria/Australia-era X-Men. I like Dani Moonstar, Cannonball, Magik, and Cypher from the original New Mutants. I like Longshot when he's not being written as an idiot, or a twit, or...well, frack it, that's been pretty much everything since the original series. I like Cyclops a lot more in the past 5-10 years than I ever did before that. I've never much cared for Gambit, Rogue, Psylocke, or Archangel. Emma Frost is fun.