Maybe h2o will have a better answer than mine, but I will give it a shot.
I think there's no simply answer to your question. Every case is different. Sometime you can get by using the Maya renderer. Overall I would say MR takes more time to render than Maya, but the result can be much better when you have stuff like glass, etc in the scene. For production render, MR is the choice. For animations, you can always mix and match both in post for the final look. The new Maya render layer engine make it a lot easier than before.
You can use most of the Maya shaders and lights for a MR render, but the truth power lays in the "hidden" MR only shaders. So MR can be a lot harder to use than Maya renderer.
As for other renderer, I had only used PRman throught RAT long time ago, so I really have no idea. Some say Turtle is fast, but I'm not impressed with the quality.