Owned the VM (50W) and tried the rocker once.
Love em both, really they are great amps.
The Orange is more versatile due to its second channel but lacks the loop of the Marshall. The Marshall has high mid focus and does an amazing hard rock tone. The Orange has a nice (though simple) clean and an addictive overdrive. The clean on the Orange could be a bit dark, but you could help that with pedals easily.
It depends on what you want/need really.