One of my favorites is probably not all that popular.
To me, he's special for a few reasons:
1) Correct me if I'm wrong, but I think he's the first original Magnus mold no? If not, he's definitely one of the first, so that's neat.
2) G1 UM was goofy, and so is this one. G1 is a brick with extendo vacuum arms. The RID one is oddly proportioned, what with his giant legs, but I find it endearing since he's posable and fun to play with.
3) DAT TRUCK MODE. It looks like he could blow through a million Decepticons without a scratch
4) The lore behind him. Not only is it neat seeing Prime and Mags established as brothers, but I like the underdogs and turncoats. He was a huge jerk, which was much more interesting than
"I can't deal with that now!" 5) He combines to make a SOOPER PRIME. He can be unstable, but still cool.
So yeah, that's my love explained