Re: Engl 50 thunder combo
NO, it's not really comparable to either one of those.
The Engl is tighter and more focused than a Marshall, with higher gain. It's not as dark sounding as a Mesa.
Engl's are great for power metal, imo.
The clean channel is very present, tho, and very nice. I would say that the Engl's clean is what a Marshall should be. As for a Fender, I would say that it's not really close. The Engl has more shimmer and greater "attack".