XI is a great game. Probably the best in the kof series. I dont know much about ether game in the technical department but they are both great to pick up and play.
TS is definitely overrated. Gameplay wise its ok. It just bores the hell outta me. And the graphics - call me picky, but they just annoy me. Horrible music too. Even street fighter alpha 2 seems better to me. Theres no way XI is any better though. 98 is where its at.
Late to the party, and I don't know if anyone's already mentioned it, but SF3 is not high-resolution (no CPS3 game is). They are, in fact, the same resolution as the CPS1 and CPS2.
And yeah, as overall solid as 3rd Strike is, I'll still take any KOF game over it. Especially XI, which has finally managed to topple '98 from its perch for me. And for those that know me, that's saying one hell of a lot.