Back in the day it was my no. 1 choice. It was (and probably still is) extremely robust. It leant itself to a kind of "get it right or it won't render at all" mentality, which forced you to be really clean and accurate with your models and mats/lights. Other renderers of the day were throwing around all sorts of tricks for getting around bad geometry but MR was kind of steadfast and stubborn, which resulted in really good results if you played nicely with it. It also had some very pioneering tools such as render subset of scene, which was missing from all other renders for *years*. That and per-object AA controls etc. I gave talks at various places on how good MR was, and I meant it.
I made the switch from MR to Vray back in around mid 2011 because I was very impressed with Vray's general speed, particularly for exteriors, and for compatibility with the pool of freelancers around London at the time, who were basically all vray trained by that point. Trying to find talented MR guys was a total pain!
MR handled/s materials and lights very nicely. I always enjoyed working with it. Did some seriously big animation projects with it and loved the workflow and results. At the time it was a very sound option for any kind of work. I've not looked at it since, so I have no idea what it's like to use these days. For me, and most around me, "unbiased" renderers are now totally feasible in everyday production, so there's no reason not to use them. Iray still piques my interest from time-to-time because of GPU-acceleration, but the current VRAM limitations still make it unusable for us. That should change soon though from what I keep hearing. Interesting to see how that will change the game!
