I chose Xenoblade Chronicles because I had to, but the character customization, the immersion, the vehicles, the side quests and affinity missions (vs heart to hearts), to basically how alive the world felt there is no comparison to how badly Xeno X stomps the original.

However, the first felt so perfectly executed. Shulk couldn't change classes, nor did he have half the abilities that Cross could have, but it felt like those were his specific skills. The world wasn't nearly as big or varied, and random nopon caravans or ganglion colonies wouldn't show up, but nothing can really beat the sheer awe of looking on the horizon and seeing the face of a God.

At the end of the day, both offer something amazing.

I love science fiction stuff more than fantasy stuff, so I'm biased towards XCX, wich is an amazing game btw, I feelt very overwhelmed by it at first, but after giving it time all started to make sense and now I completely adore it, is a really rewarding experience.

The first is the best by a good bit.

However if you own a Wii U you owe it to yourself to get this game (XCX).

Xenoblade wii without a doubt. It's a 10/10 game for me, it's a pity it has such graphics but well, it's a masterpiece anyway.
As much as I like Xenoblade X, the continents are gorgeous and I have a blast exploring them, but the story, characters and above all, the music, are far better on the wii game.
I'm not a big fan of remasters, but I'd do unspeakable things to get it remastered for the NX. If they can make a game with all the great things about xenoblade but with the scale of X, I'll be the happiest man alive.

You forgot music. The first games score is beautiful and as good as some of the old FF games.

The original is better in most respect. The combat system in X is better until the postgame, but after that it again falls short to X. None of this is to say that X is a bad game by any stretch, and it does a few things better, but the original has it beat.

I prefer X music actually. Not a popular opinion, but I love how they mixed a lot of styles on the OST, and it's very unusual for a RPG game. 

Xenoblade Chronicles X is much better.

Xenoblade Wii ranks last in the series for me. I still like it, but it is not better than any of the other Xeno games.

Not even Xenosaga Episode II? :P 

@OP I'd rank the games like this. Xenogears = Xenoblade (for different reasons) > Xenosaga Episode III = Xenoblade Chronicles X > Xenosaga Ep I >> Xenosaga Ep 2

The original was better for its story...

But I prefer pretty much everything else in favor of X.
So my vote goes to X.