Mini T has been discontinued by Petzl now I think so the choice is mainly Pro vs Micro for new gear. Sure there are a few Mini T's left out there though.
My experience... Mini T is favourite, easy to use with and without gloves. Micro T more fiddly and will engage itself more easily which is a pain when I just want a pulley or to release it. New Pro T = sexy, slick, but like a brick on your harness. Old Pro T = easier to use then new one but need an extra krab.
The bigger the wheel the better in the case of efficiency and rescue, which is after all why you carry one. Bearings of courses play a part too. I think the new Micro is more efficient than the old Mini, but I still prefer the Mini.
As you probably guess I have one of each! Micro on my personal SRT kit, Mini for Wales work and Pro for all L2 and SRT where I might need to pull people longer than a few feet.