Try both and see what you like, but I prefer cranking the master to my desired saturation level and using the output knob to tame it. I suppose they're two different strategies though. One problem with cranking the master is that you can have volume level differences in live use. By cranking the output and adjusting the masters to taste you can have a more uniform volume level between channels. I'd rather take the volume level differences because the tone is just better when you crank the master IMO. Also just a beginnner Mesa tip (I've only recently figured this out), try cranking the master quite a bit and THEN adding gain to taste... you get your power tube saturation more easily that way and its a much clearer tone than using the Gain knob too much. One easy trap to fall into with Mesas, especially Rectos, is to have way too much gain without even knowing it. For Modern on my Roadster I run the gain at around NINE oclock but have the Master at or above 12. Experiment around, but I've found that even for metal the most tasteful tones only require a quarter to a half turn worth of Gain (and I use low output pickups).
