UM looks better (my personal opinion) and when you see UM up close you realise there is definitely more to him than meets the eye... he's lovely and heavy as he's made with metal and looks like he's just walked out of a G1 cartoon. And of course he talks which is a GREAT conversation starter when you freak people out.

However this guy despite looking a bit plasticky irl (especially around the arms and autobot logo) is going to be more articulate I am sure and so might be fun to pose and be more hands on to play with.

Here's a few pics I took of MAS-01 at HKACG:





He is a little bit like Ben Affleck's Batman - a bit TOO chunky in proportions, whereas UM is just like an oversized MP-1 but I quite like the exaggeration of MAS which is why I am seriously considering getting him to contrast with my other figures... and the price is almost too good not to get him.