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You want my honest, personal opinion? I jumped from gen 3 to 6 with X/Y...
X/Y is pretty enjoyable during your main playthrough, the story is meh but once you beat the Elite Four there's only one small sidequest you can do & then the game's over. So unless you're into competitive battling, skip X/Y.
OR/AS is probably better due to nostalgia but I don't have it so I'm gonna talk based on the facts alone. It has some new features but lacks trainer customization & Friend Safaris which X/Y had, its post game isn't that much better save for another side quest & many old legendaries roaming Hoenn. All the R/S/E legendaries are available in-game plus Deoxys & Regigigas. It doesn't have a Battle Frontier.
However it has online Secret Bases so you might be interested in those, plus you get a free Lati@s in-game which you can actually ride on & explore Hoenn more in the post-game...
In case you wanted hacks, I'm currently playing through Prism & Maize, these 2 hacks are pretty solid with actual new features so you should definitely check them out.