One Winged Angel
Yeah... So given how often I've heard both of these, I did my usual "play them back to back while doing other stuff and see which one you remember more of" test. And listening to One Winged Angel... there's this anticipation throughout the entire thing that just isn't there for the FFVII Main Theme. I spend most of it like this: "yey! it's the build up to 1:10, whee! now we're at 2:15, nice! some downtime at 3:00, oh! let's rock out to 3:22!, now we get to start all over again!".
The FFVII Main Theme is a great theme, but it feels a lot more passive then One Winged Angel. It's one of those themes that sounds great when I hear it, and is obviously a well crafted theme, but it doesn't really grab me. One Winged Angel grabs me. A lot.