The best advice I can give is get out there and try as many as you can before you buy.
Amps are strange critters, what sounds superb with one guitar won't with another. What someone tells you is the bees knees you will think sounds like a wasp.
Personally I won't touch a Mesa with a barge poll, much preffering VHT's, however you could try examples of both and love the Mesa.
Because of this dilemma I have many amps. It's the only answer!
Having said that, a good two channel amp with a boost pedal will cover the same ground as a three channel beast. A pre-amp pedal is another option, such as the HBE Dos Mos which will drive a clean amp into break up. Leaving the drive channel for heavier rhythm and lead tones. A good overdrive pedal will do the same thing (the Dos Mos does not colour the sound though).
Also when trying, take you own main guitars and effects. Getting to know what it will deliver with your own kit is half the battle.