If you need a quick good sounding Ampsim choose Amplification Lite. It is a Amp with 3 Channels - Nothing more but all you need if you want to work quick. Not so flexible like other Ampsimulations and there are no internal modulation effects. The internal Cabinet Simulation is quite good but external Cabinet Impulse Responses can be loaded in.
The Sound in my opinion is near on my real Peavey 5150 Stack.