I think it's reasons like trying to compare FF6's and Chrono Trigger's soundtracks that I see a lot of people simply say they like the composer. Nobuo Uematsu did both, right?

That's like comparing Indiana Jones to Star Wars (the good trilogy) in the music category. The reason that there's such a strong similarity of songs between the two games (including having the battle theme be weak in both) is that the same guy did it.

That being said, I can understand how one person could have a completely different opinion of one game in contrast to another. Chrono Trigger's soundtrack happens to be a more upbeat track, much like it's a more upbeat game. Compare the "positive" overworld themes. You've got Tina/Terra, which is just Terra's theme given a distant wind instrument effect, then you have the cheery 1000 AD, where there's a freakin' festival going on.

Frog's theme is one of triumph, because you KNOW he'll succeed. A character early in the game tells you that. Cyan's theme is not as much so; it's more one about overcoming adversity, which you hear halfway through the theme.

I tend to find Chrono Trigger's track a tad superficial, but that's not necessarily a bad thing. The point of the music is to set the theme of the character, area, or situation. Superficial works because you get the general idea really fast.

Final Fantasy 6 has a little more meaning in the songs, but it's not a very upbeat track. There's a powerful empire terrorizing the globe, they're on the brink of war with a subterranean discovery, and things are just overall kinda crappy.

Schala's theme was one of my favorites in Chrono Trigger. Most character themes in both games were among my favorites. I don't know if that's because it brought the character to mind or if they seemed to be the most emotionally involving of the tracks.