I will give FFXII points for Vaan as compared to Tidus though. When Vaan acts dumb people at least call him out on it. (see his asking Fran how old she is)
Whereas Tidus...well, he actaully sniffed Auron one time. he literaly bent over and started taking giant whiffs of him.
At this point the acceptable reaction for anyone there would ahve been to beat the living hell out of Tidus. Maybe break a limb, fracture his skull, God knows brain damage wouldn't even show with him.
But no, Tidus gets away with acting like the world's biggest spaz.
The rest of your post is opinion, so I won't argue with that since you have the right to the opinion that FFX doesn't feel like a FF game (I personally disagree with you, but to each their own ) But I have to say something about this point; and would like to point out that Lulu has, on a few occasions, called Tidus out on being a dumbass. So I don't really agree he totally get's away with being weird and spaz like. Lulu put him in his place a couple of times. She also put Wakka and Yuna in their places too.
Moral of the story: Lulu's badass.
But back on topic:
It depends on your preference. If you're into love stories, or a game that focuses on telling a story then go with X. If you're into political issues, a very deep and mature dialogue then go with XII. I personally prefer X to XII because XII just plain bored the hell out of me. But that's just my opinion on it. At the end of the day I suggest playing both of them, along with the rest of the franchise.