I don't really like 3D much sorry :P Graphically, I think Gen 4 and 5 were the peak of the series - Gen 6 looked okay, though there were definitely scenes that looked terrible, and while Gen 7 looks amazing, it can't beat sprite and tile-based graphics for me.
Graphics aside, I'd put Sun & Moon second or third on my list of favorite games, with ORAS... I don't know where I'd put them, somewhere in the middle-top I guess, and X and Y at the very very bottom. So overall, I suppose I like the 3DS games less than older titles, haha.
I wanted to elaborate on this because I HAD MORE THOUGHTS! but now I'm tired so will continue this tomorrow goodnight.