I have to go with Ken I have played Capcom vs. SNK 2: Mark of the
Millennium 2001 and SNK vs. Capcom: SVC Chaos and on both Ken is way
better. His set is better and he hits way harder than Terry. Terry is the best in SNK but SNK fighters don't have anything on Street Fighters and the games prove that over and over. As for in the movies Terry does fight some impressive people. One the other hand Ken fights M. Bisson and Ryu and during his fight with M. Bisson inStreet Fighter II: The Animated Movie he overcomes spinal paralysis with his Chi. He also can become Violent Ken. An alternate version of Ken. (This came off of the Ken Wiki I'm to lazy to parapharse it) It is implied in SVC Chaos: SNK vs. Capcom
that Ken possesses the Orochi bloodline and Violent Ken is a
manifestation of this, much like the SNK characters Iori Yagami,
Yamazaki and Leona. As a manifestation of the Riot of the Blood,
Violent Ken also used purple flames instead of regular ones in his Shōryūken. Therefore because Ken possesses this bloodline he is actually slightly stronger then his friend Ryu.
My two favorites from both games so its a hard one to call but ima have to give it to Terry. Ken is my number 1 dude but i think Terry wins becuse he is more versatile. In the games and the animes he has a greater number of moves for different sitations. And i belive this give shim the edge he needs to beat ken.