Syndrome, easy. Dude might have a petty reason for his crimes, but he's still a damn genius and he was close to be successful with his plan.
Billy has a tiwsted, but still a motive. Stu is, well, a deranged psycho teen without any redeeming qualities. I think that Billy is a bit better, but only slightly.
100% Lotso, Miles isn't that good in my opinion and his writing is meh. Lotso is better written and he's more sinister.
His name is weird, especially knowing that Marvel already has a villain who's named Thanos. Coincidence or intentional copy from "Squid Game" authors?