I think if the goal is to be distinguishable, then only Beam (and maybe Bauhaus) meet that. To me at least, the different marbles are forgettable - if the goal of an avatar is to appear next to a name and help me realise it's the same person who also wrote that other post, or a different comment, or the OP, then they need to be individually distinct enough.

Beam definitely meets that criteria (there's nothing like faces to trigger your brain's distinguishing algorithm), and Bauhaus could do (although I'd add a few more colours into the mix, and maybe not use all of them in every avatar).

The rest really don't.