Robin Wright -- Out With Hot New Fiance ... While Sean Penn Hangs With Charlize

It was the BATTLE OF THE REBOUNDS in Hollywood last night ... with Sean Penn and his ex-wife Robin Wright each hitting the town with their new hot significant others -- but who came out on top?

Robin hit up RivaBella on Sunset with her "Lone Survivor" fiance Ben Foster -- he's attractive.

Sean went to his Help Haiti Home gala with new rumored GF Charlize Theron -- she's also attractive.

It's been almost 3 years since Sean and Robin finalized their divorce, but you KNOW they're judging each other's rebounds ... because that's what exes do.

So, we gotta ask ...