Guilty Gear is popular enough that you can pretty much plug any track name into youtube and hear every version.
I don't know how others feel about it, but while I love most of the series music (and found the Korean tracks a delightful "interpretation", so to speak), my favorite is still the original Guilty Gear Original Sound Collection (which is probably pretty hard to get now). Back in '99 or 2000, stuck in study hall, had my first MP3 player (CD-based!) and listened to a random album I grabbed back when nobody questioned FTP downloads as the primary option for non-Japanese obtaining the music. I was hooked from the first track.
(incidentally, that excellent first track was cut from the Sound Box release to make room for the character ending tracks, which had previously been left to a separate CD. I think it may not even be originally part of the game, but I haven't played GG, so I wouldn't know.)
I also rather grew to like the Isuka score over time, even though it's more experimental than the regular stuff. "Sheep will sleep" and "Riches in me" are favorites of mine. I didn't really like the extra tracks that were added later, though (Fill de vent, Quicksilver, etc), but I suppose I haven't really given them a chance.
"Guilty Gear XX Sound Alive" is a live concert album, which I'm usually not that fond of (with some exceptions), but there a few VGM-listening feel good moments as when the audience audibly cheers for the final song (track 21).