Pokemon X or Y? It's the question of the weekyear. So many times have we spoken of Pokémon X and Y, but now we're down to the wire. The game comes out in a week, and we know more information all the time. It's time to choose: which version are you going to get? It comes down basically to three things: the version exclusive Pokémon, the version mascot (Xerneas and Yveltal), and the Mega Pokémon. Let's look at each.
Pokémon X or Y: Version-Exclusive Pokémon
The most important factor in choosing between Pokémon X or Y is version exclusive Pokémon, as it has been for every Pokémon game since the beginning. But, unfortunately, we know surprisingly little about the version exclusive Pokémon. Of the many, many Pokes that have been revealed, we only know four version exclusives for each generation.
Pokémon X version exclusive Pokémon so far: Xerneas, the legendary stag; Clauncher, a Water-type lobster and the Water Gun Pokémon, and Swirlix the Fairy-type Cotton Candy Pokémon and its evolution Slurpuff the Meringue Pokémon. More on Xerneas below. The other two aren't anything terribly special, and each has a clear counterpart in Pokémon Y. The three known Pokémon Y exclusives are Yveltal, the version mascot Destruction Pokémon, Skrelp, the Water/Poison bit of algae, and Spritzee and its evolution Aromatisse, respectively the Perfume and Fragrance Pokémon, and both Fairy-types with the Ability Healer.
Honestly, of the many cool Pokémon already announced for Pokémon X and Y, very few besides the mascots are version exclusives. I'd say Pokémon Y has the lead at the moment, since Swirlix the Cotton Candy Pokémon (exclusive to X) is pretty lame. Basically, we don't have enough information to make a call here. There will be lots of exclusives that we simply haven't met yet.
Pokémon X or Y: Version Mascot
The version mascots look like they're going to be exclusive to either Pokémon X or Y this time around, and even if you don't care about legendaries, each one represents a certain sensibility that will be loosely reflected in the games. Xerneas, the Fairy type legendary stag, is exclusive to Pokémon X; Yveltal is Dark/Flying and officially the Destruction Pokémon. This suggests that Pokémon X will have a loose theme of order and preservation, and Pokémon Y will focus on chaos and destruction. If you have a preference one way or the other, that can help make your decision.
It does for me: I'm getting Pokémon X entirely because of Xerneas.
As for Pokémon Z... that's another story, but you don't want to wait a year, do you?
Pokémon X or Y: Mega Pokémon
It's the mega Pokémon that really throw some added spice into the Pokémon X or Y decision. That's because this is all new: Mega Pokémon, new to this generation, will sometimes be unique to one version. Well, not quite: the item that evolves certain Pokémon will be unique to particular versions. So far, it's only definitely confirmed for Mega Charizard X and Y and Mewtwo X and Y. Mega Charizard X's mega item is only in X, and is Fire/Dragon with the Ability Tough Claws. Mega Charizard Y's mega item is only in Y, and is still Fire/Flying, with the Ability Drought, and the second Ability Not Being As Cool As Mega Charizard X. Mega Mewtwo X is Psychic/Fighting.
Personally, I think that, as far as Mega Pokémon go, the Pokémon X or Y question goes firmly to Pokémon X. But your mileage may vary. Even more so, there may be more Mega Pokémon exclusives we simply haven't met yet -- most likely for Blastoise and Venusaur (why does Charizard get all the love?).
Pokémon X or Y: Conclusion
It probably won't surprise you that there's no clear call between Pokémon X or Y. But, since we know so little about the version exclusives, it comes down to story and theme. Black and White, and Black and White 2, had different themes between versions. It's not immediately clear whether Pokémon X and Y will follow that tradition. But considering the legendaries and the world of Kalos, it seems pretty likely.
Which version are you going to pick, and why?