I've never played one personally, but back in 2006-2007 I went to quite a few shows at Harpo's in Detroit. Many of the 'local' bands that came on before the international acts played thru Peavey ValveKings, and they all sounded bad.
It could've been that the local acts didn't get a soundcheck, or the guitarists that used them didn't know how to dial them in idn_smilie But it seemed like every local band that used Marshalls, Mesas, or Engls always sounded better.