I have flown on...
737-200 (Delta and United)
737-300 (Southwest, United, US Airways, America West, Frontier Airlines)
737-400 (Alaska, US Airways)
737-500 (CanJet, United, Continental, Southwest)
737-700 (Alaska, Southwest, Continental) with winglets and without
737-800 (RyanAir, Alaska, Continental, American, Delta) w/ winglets and w/out
737-900 (Alaska, Continental)
Out of all of them, my favorite is the 737-700 with winglets. Maybe that is because I have flown it in an actual AS
simulator, but it I like it a bunch. Long range, cool looking winglets, and great performance. Not a huge fan of the 2X2 exit row config though.
737-200 (why not)?
737-500 (that thing hops)
737-800 (seemed cramped to me)