Well, reading only the 1st page of this thread and not the next 3, I have several points to make.
1st off... the mesa is not muddy. At all. None. If it is turn the bass down, you are crazy. Period. I can say this because... I have 3 of them at my house right now. An older dual, and older triple, an a new dual 3 channel.
The Marshalls are inherently more muddy than Mesas. I can say this because I have owned 2 Marshalls, have tried out about 300 of them.
Now, I like a good Marshall tone. BUT... Marshall QC sucks. Do not argue this fact for it is true and anyone will tell you this and you can prove it to yourself by walking into a big dealer, turning on all the identical marshalls, and playing through each one. They will all sound different, and half of them will suck. Yes, they will, cause I have done it, several times, as have about 1,000 other people (go to RAP and do a search). The mesas on the other hand, will all sound identical, as the 3 at my house do, and they are seveal years apart in age. That, my friend, is QC.
Next point... there is no such thing as a "Marshall" switch on any of the Mesas, or even anything vaguely resembling that. You must have had a line 6 and mistaken it for a Mesa. Bad call.
Sometimes, I would like to have a little bit of the Marshall (ahem GOOD marshall) midrange, but shit, the Mesa just sounds great, and for modern rock it unbeatable (not unmatchable, mind you, you can do just as well with a GOOD marshall) except with a Bogner Ubershall, which is just plain unbeatable period by any mesa or Marshall. The Rec is modern sounding, and sits in a mix like a motherfucker. No other amp I've tried sits that way right out of the gate, and I have lots of amps roll through the studio every week, and most of them end up paying my $15 tube charge and using my Mesa in the end.
If you want more of a marshall sound from the mesa, turn down the presense, gain and treble, turn up the mid some, and there you have it. Want more of a vox clean sound? Switch to spongy and tube rectifier mode and voila.
The Mesa has way too many settings to say it doesnt do shit next to a Marshall, which has none. If it seemed muddy or boxy to you, it was probably on sponge and tube rectifier with the gain too high for that setting. It adds a weird low mid that can be kinda weird for heavy tones, but perfectly awesome for clean tones.
Know what you're doing before you make crappy uneducated claims as fact on a board where people take your ideas and make high dollar purchases based on them. Thats a shitty thing to do to someone. I would be PISSED if someone here talked me into buying a Marshall instead of a Bogner because they swore by it and never heard the Bogner. A million people claim the 57 is the greatest mic of all time. Well, having used it against every other mic I have, I realize that its the worst of the bunch, and no its not a bad one. I should kill everyone that made me waste $75 on that mic, but it does come in handy here and there when I run out of good mics.
By the way, Bogner rules. I would sell my Mesa in a second for an even trade on an Ubershall.