they both are 2 stage heating system and good at that. the 58mvc model is the infinity 95% afue, and the 58mvb is the variable speed 96% afue. They both are good, but I like the capability of the mvc model.
The Infinity/Evolution control is the most versatile & user-friendly I have seen yet. I have one (Evolution) in my home and really dig it. Just make sure you choose an installation contractor with a good reputation, who really knows what they are doing.