The Hiwatt is more clean than most Marshalls from the 70's.
Plus is has a bigger slightly more dry tone.
Both sounds positivly great.
Cannot say much bad about either brand
Depends on what tubes you use, but has a different overdrive than the Marshall.
But everybit a loud and full, actually do not stand near it when it happends, I know from firsthand experience that it is insanely loud...