TNG is more vanilla, thus more appealing to the masses. But ratings success can not be the final say. Because, as I have mentioned elswhere, Baywatch got higher ratings than TNG. So does that make Baywatch the better show? I hope not.
And it must also be pointed out that TNG came around with very little other choices to watch in terms of first run sydication and network scif. DS9 had to deal with SEAQUEST..BABYLON 5..Stargate.., not to mention TNG, and far more sydicated competition.
TNG, to me, never had really deep character growth. It has some, but not as much as DS9. DS9 is great because everyone, from Sisko to Nog, grew in ways no one could have predict. When you can't predict where a show is going, I think it mirrors reality.