It's not on your pole but FFXIV's Nail of the Heaven's is pretty epic with it's metal guitar.
For the convenience of others, this is a medley of the 14 FF themes.
I don't really care for Normal Battle themes, I've played these games so many times I just can't help but have my mind go into auto-pilot while I listen to them so I can't really say I like any of them because none of them can really keep my interest for long to appreciate them.
I should've done my research, sorry. i wasnt aware that an MMO would have a battle theme, sort of like 12.
I'll promise to look more carefully with the Boss theme's