You can possibly look at bands with the same style, e.g Dream Theater and Symphony X, but to compare Theater and metallica is a bit ludicrous.
everyone shifts from liking one style and a couple of bands to another style all the time, i could be listening to Racer X one moment and then some Bach the next, but i wouldn't be able to say which one is the 'best' because that's just not the way to view music.