Might as well draw many more renderers in this battle, but lets add Final Render to it as well.

Now:

Maxwell:

Physically correct renderer. Computes light as it would travel in the real world, and, if you leave it on enough, no noise- no nothing. Never will it have blotches, since those are Photon Mapping caused artifacts. Maxwell runs on edited versions of the Metropolis Light Transport algorithm, called ER (I don't know what it stands for). However- the MLT or ER algorithms are... slow. but they are unbiased. Well, compared to other algorithms they are fast, but the industry leading standard is Photon Mapping, and that is really faaaaaaaast. MLT or ER isn't really faaaaaaaaast. Also- MLT and ER are not so good at caustics- though Maxwell might use photon mapping for caustics.

Mental Ray:

Store brand photon mapper. It is super-efficient, but its artifacts are splotches. It is not unbiased becuase photon mapping is only an approximation of the rendering equation (light situation and radience transport that describes how light goes around in the real world). Mental Ray is efficient, fast, and mostly, an industrial standard (mostly, and I think so, correct me if I'm wrong), since Mental Ray is inset with Maya and 3ds Max.