The main four boys have all been my favorite at some point over the years, but currently it's Damian. I find him so funny, especially when an artist draws him like Calvin from Calvin & Hobbes. His emotional journey's been really satisfying to watch over the years, too. imo emotionally complex child characters are pretty rare, and when Damian is written well, it's fantastic.

Just for fun, I'm going to add in other media versions of Robin.

Favorite animated Robin: Tim from the Bruce Timm universe (idk what it's called). He was so cool and his episode with Superman pretending to be Batman was a classic. His fate in the Batman Beyond movie was more tragic than anything that's befallen the comic Robins. (Runner up: the Teen Titans Robin)

Favorite live action Robin: Burt Ward. No contest.

(Ironically, I think my least favorite animated Robin is Damian from the movies. lol He's so OP and unfunny in those. Needs more Batcow.)