A couple of things about the Tech 21 stuff:
The Mesa settings are based more on the Mark IV, NOT A RECTO! Deeper voice, nice and smooth. For Metallica, it will do MOP and AJFA types of sounds if you have a pickup that is hot enough. Most people would probably still want a distortion pedal in front of it.
The Fender channel sounds good, but there is a BIG volume drop when switching from one of the other channels. That sucks.
The Marshall channel is cool, and it covers a lot of ground, unfortunately clean is not part of that ground. The Mesa channel does a pretty good clean, but not the Marshall channel. I don't think Marshall amps have ever been known for their clean sound, though.