ACE+ and co. made a tremendous composition which suited the fantasy/mild sci-fi world of the Bionis/Mechonis remarkably. The game opens to a soft piano and violin piece simply entitled "Main Theme", by Yoko Shimomura, which showcases the tempo that the majority of the soundtrack takes on. The adventure begins with Colony 9's bouncy theme and gets carried over with the likes of the catchy Gaur Plain, the mysterious Satorl Marsh, the tribal Makna Forest, and the tranquil Eryth Sea, among many others. Overall, Xenoblade's quality of sound is what most RPGs should strive to reproduce, although many have gotten quite close... Last but not least, Yasunori Mitsuda (composer of Xenogears and Xenosaga: Episode I, by the way) provided a solitary contribution to the soundtrack, the ending theme entitled "Beyond the Sky", which is performed by Sarah Àlainn. It's quite possibly the most evocative track in the game, and stands out alongside God Eater's "God and Man" and Final Fantasy VII's "Eyes on Me".
Hiroyuki Sawano's take with Xenoblade X has been a target of much debate about how discordant his style is compared to the original music. But most people fail to realize that this is not going to be the same game, as practically all attributes relevant to fantasy have been replaced by a science-fiction atmosphere. Sawano's massive usage of sweeping orchestras, epic choirs, electric guitars, and techno undertones brings out the intended sci-fi approach in tracks such as "Codename Z". Also unlike the original, he incorporates a multitude of vocal themes ranging from driving metal/rap (Black Tar), dynamic dance music (Don't Worry and Wir fliegen), and an introspective rock track (The way), to name a few. Another strong point is the field themes (or one field theme that I can pick out from the track names), particularly "Field Kaijou", a serene desert-like piece interspersed with something like Arabic chants and an almost haunting melody. As my favorite composer, personally, Sawano has succeeded in replicating the same sense of awe that I feel when listening to Attack on Titan or Mobile Suit Gundam Unicorn, so needless to say I think his work fits in with Xenoblade X immaculately. Sure, there's a fair share of filler tracks, but the majority of it is enjoyable, to say the least.
Who do I think is better? Neither. Both groups have achieved the perfect blend of unique elements which bring life to the final product. Just as Yasunori Mitsuda and Yuki Kajiura before them, the Xeno series continues to flourish musically. If given the choice, I'd select any one of them, or possibly a mixture.