"Shouldn't we consider the danger of the species as well? I keep croc monitors and Lacies, and I love lacies, but they can bite the holy dogbeans out of you. Either on purpose or accidently."

I certainly agree with you there, but was simply responding to the original poster's request:
"Monitor size and enclosure needs aside, which species make the most rewarding captives?"
I think lacies are the most rewarding captives, but I'd never recommend one as a first monitor. My adult male, Alex, is easily the most dangerous animal I've ever kept because he's probably one of the seemingly 'tamest' reptiles I've ever owned, but has a hair-trigger feeding response that's nothing short of scary.