I've had 3-4 Monarchs and a couple 3200s and 4200s. I would say the 4200 and the Monarch are very comparable. The 3200 is more comparable to a Prostaff than a Buckmaster IMO, glass-wise.
I'm not a fan of the higher powered models of Bushnell or Nikon. That said, the Monarch and 4200 3-9x40s are both very good scopes. I think the 4200 can be had for less($200), so that would be my pick of the 2. The reality is, however, I would rather spend less and get a Weaver Classic, which is every bit as good or better than both, IMO. When I go "higher" than Weaver, VX2 is the next step......