The King of Fighters series is amazing to me. It seems like I'm the only one who feels that way. Street Fighter, King of Fighters, and Tekken are my favorites...to be specific: Tekken 5, KOF 2006, and Street Fighter EX2 Plus.
But, I have to say...MK Armageddon is pretty incredible. 60+ characters?! Who does that?!
Street Fighter 4 I think is a really good game. Guilty gear XX Accent Core Plus is technical I think. I never got into that one. I find myself play Street Fighter 4 hours on end just beating people down to a pulp with my boy Balrog on the PSN.
I cant really talk about fighting games of modern times as I have moved away from them somewhat, but I can tell you my all time favourite fighting game, street fighter 2 turbo for the super nes, get that in ye!!! lol.
I would have said Street Fighter IV like a month ago but I'm starting to hate it really badly. I've always loved Mortal Kombat and Super Smash Bros, and I'm pretty sure I'm going to buy UFC undisputed if it gets solid reviews.
For me, the best two fighting games IMO are the Tekken series and the Soul Calibur series. I don't agree with people saying that Soul Calibur is just for button mashing people, for the simple reason that you tend to do the same moves when doing this.