When it comes to logos I'm pretty conservative and old-fashioned.
I think the best is certainly the one of Darkthrone.
For me it represents the special atmosphere of (the early) Darkthrone just perfectly. What's more it fits greatly above any b&w picture of a forest (which is the best alternative for a CD cover IMO
On the other hand I like Varg's point of view - simply not using any popular symbols (pentagram or inverted cross) in order to be different from the rest of metal bands of 90's.
I don't like Immortal's original logo - it is over the top IMO - too comlicated and too "fat"... looks like a bad ghetto grafiti.
Two logos that I really hate are Judas Priest's and Sodom's...