I prefer the Final Fight series. I grew up with it and I may be biased. I've only really played different versions of the first one though (SNES, Arcade, GBA). I haven't really played FF2 and 3. But yeah, I'm a big fan of Final Fight.
As for Streets of Rage, I played the second one on PC a few years ago. I thought it was okay. It doesn't help that the fanbase overrates it. But anyways, I recently bought Streets of Rage 1 because I was in the mood for a beat 'em up and because it was only $1 and I enjoyed it more than I thought I would. I don't know what happened. I also ended up buying Streets of Rage 3 to play later on.