On the whole, I do think DS9 had the best cast, as far as the talent of the actors. The TNG characters are all likable, but they're also relatively bland for the most part, and the roles are less demanding. The actors also tend to do less with what they are given. Stewart and Spiner are the standouts on TNG and, while what Spiner was able to do with Data is certainly wonderful, as far as how charismatic and charming he is while playing a robot, it doesn't really vary or evolve very much.
Nobody on TNG does anything that even remotely resembles what Nana Visitor was able to with Kira over seven seasons, for example, as far as creating a fully fleshed out character (she does benefit from a lot of very good writing, also, though).
Totally agree.