I wouldn't say that they have the best, some are really good, especially the stuff for Hellsing Ultimate.
I'm just a sucker for awesome instrumentals.
And yes just as Liege says, translate most of them and you get the most gayest, crappiest and most horridly out of place themes ever!
but that doesn't mean I hate all of them, I think the song to GANTZ! Super shooter is quite awesome, just have to figure out what the lyrics are, most probably they will make it crap
Anyway I still think shows are better off with opening themes that don't have song in it, like Beast Wars, Batman TAS and Hellsing.