The most versatile would be RAT, but the learning curve is steep, especially when it comes to writing your own shaders. And the price tag reflects its versatility
The latest version has all the bells and whistles like GI, caustics, etc., but it's also one of the smoothest renderers you will ever find. The main difference is that MR is integrated into Maya ( except for things like Fur, particles, and Paint Effects), RAT is more like working with a seperate app. Not only must you use Slim ( the Rat shader tool) for all texturing, you must also link your Maya lights to Slim lightshaders. But on the plus side you can use Alfred for batch and distributed rendering
Red bellows of flame have blackened my stones
Convulsing my frame and cracking my bones
Hell's dragons of steel who roar in their chains
Crawl into my caves to suck out my veins.....
-The Mountain P.F.M.