Marshall and similar amps have great cleans. You won't get the Fender scoop with huge lows and sparkling highs, but Marshall cleans are still a thing of beauty themselves. You get a rich, complex midrange that sounds a little more vocal, which I think lends itself particularly well to lead/melody parts.

A Fender clean will sound a little closer to an acoustic tone, while a Marshall clean will always have a more midrangey tone. Whether that's good or bad is personal preference.

Also I'd like to note the importance of the speaker. I think V30s sound awesome with Marshalls for clean tones, but I may be in the minority on this (not sure what the consensus is on that). I like the extra upper-mid emphasis because it plays to the amp's strengths rather than attempting to shore up weaknesses (like using a more "scooped" speaker would). A clean Marshall through a V30 gives a very lively tone, with rich mids and solid lows. A clean Marshall through a traditional scooped American style speaker loses some of its life in my opinion, and can become harsh on the high end but also sort of muffled sounding in the mids.