Go with Mesa. In mt opinion, they sound a lot better. Also, a ton of people use Mesa-Boogie amps (the ...And Justice For All, Master of Puppets, Black album tone was made with Mesa Mark-IIc amps.
Actually, since that's just my opinion, play them and decide which you like better. Try out a Blue Voodoo too, they sound really good and cost less than Marshalls or Mesas.