I like the strongest party:
Cloud, Barret and Cid
With Yuffie as an alternative.
However I also like a storyline team (have Cloud and Tifa):
Cloud, Tifa and Barret
Alternative: Cid
Or just a fun team:
Cloud, Tifa, Yuffie
Alternative: Cid

I have never thought highly of Vincent's character or Red's. Red XIII is fine but doesn't have much feeling or character build outside of the Seto thing, which I feel is kind of empty because there's no feeling between his love and hate of his father. Vincent's just lacks much meaning, though I may start to like him more after DOC. Cait Sith is a character I like but not in battle. His limits are pathetic (or overly powerful) so I've never been interested in using such a character. The others I like, Cloud, Tifa and Yuffie being my favorite team.