Amplitube is awesome but too much low end on everything for my tastes. I'm a Guitar Rig fan, and lately I've been getting wicked results from combining different amp sims on a single guitar track: my favorite set up for high gain/metal tones is Guitar Rig + Vandal + Pod Farm. The resulting mix is a crushingly heavy tone but not too muddy or discordant.

By itself, I think Vandal's metal tones are better than all the other amp sims, but they kind of all sound similar--but mixed with a heavy guitar rig tone, you can use Vandal's balls without sounding generic.