What makes it your favorite? Do you want to play it? If so, what's keeping you from doing it?
For me, it's Burning Wheel.
I bought it purely based on aesthetics back in 2008ish, then got the supplements, then Gold, then Gold Revised, with the Codex, and the anthology...
I blame it for my weakness for chunky, digest-sized, hardcover RPGs. :P I also like the graphic design, I like the prose (even if it's divisive), and it has both interesting lessons you can plug into other games (like "let it ride," letting success or failure stand instead of making lots of little rolls) and arcane systems that pique my interest (like the Artha cycle, which makes roleplay, metacurrency, skill rolls, and advancement all intersect). I genuinely like reading it for its own sake.
I haven't played it because... well, since it's not D&D, that immediately makes it harder to get people interested, sadly. It's also a bit daunting, given its reputation as a crunchy system. But I have a group of players interested in trying new things, and fewer other games calling for my attention, so hopefully I'll get a chance soon. :)
I've watched people play MOTW and Paranoia. Both look plenty fun.
I'd also love to try one of the WH40K RPGs, but they seem like a big commitment. And like you said, it's a lot harder to find people who want to go beyond D&D
I've had the change to play Paranoia, actually! It was a ton of fun, and one of my favorite gaming memories. It ran great as a fun one shot.
I've had ambivalent feelings about Paranoia for a long time. I love the setting and it's inspirations (especially Terry Gilligan's Brazil). I have the XP edition, and the rules were confusing to the point of causing me drowsiness. I think they just put a rules section because they had to, and the GM is supposed to fly by the seat of their pants based on what is the most fun.
That said, I'd love to try it.