I have avoided this thread on purpose. It is too hard to choose just one since tastes change over time. As of today, my EBMM Petrucci has been my #1 since 2000. Feels, plays and sounds great. I hardly ever play any Dream Theater. I'm sure if I was to play a customized Suhr I would change my opinion.
If I was only able to have one amp I would have to choose the Mesa Mark IV. It is my favorite amp I have owned/played (Peavey Butcher, 5150 II, XXX, Line 6 Vetta, Vetta II, HD-147, Framus Cobra, Engl Powerball, SE, VHT CLX and Mesa Mark IIC+) up until now and I could easily play anything I want with it. Case in point, my opinion may change once I get my Marshall JCM800 Fortin Cali mod back. I have a feeling it will!