Honestly, X is the best Pokemon game I've ever played.
Omega Ruby is pretty good, but the Experience share issue is more pronounced in that one, and I don't think you'd fully appreciate the changes made to it unless you played both a Gen 3 game and X or Y first.
So I suggest playing X or Y first. The amount of pokemon you can get for your team in the base game alone is staggering, I personally enjoy the pacing way more in terms of progression from location to location, you pick up both a Kalos and a Kanto starter before your first gym, and if you're going to get to grips with the new Fairy type, the game is structured around it.
Compared to Omega Ruby. I'm not bashing it in any way, but it kind of assumes you've played X already, so doesn't go into as much depth with what fairy types are, or why Mega Stones are a thing.