i think i know what you mean but if you could elaborate more. i always said 97 controls the smoothest out of the whole series. when playing with a stick i can't tell much of a difference between 97 ans 98, but i really noticed when playing with a pad how smooth and easily moves could be pulled off.
I think there are multiple things that contribute to the smoothness. One is it's easier to cancel moves. So, for example, the classic jumping kick, crouching poke, fireball, dragon punch combo. For some reason it gets way easier to pull this type of stuff off in '97. Another is how it seems easier to get into a groove. Running, hopping, etc. commands just seem a lot more responsive. I've never felt as comfortable with SNK fighters as with Third Strike. I can't quite put my finger on it, but I always get that "it's on the tip of my tongue" type of a feeling with these games. With '97, XI, and XII in particular, I feel the closest to "getting it".