Greatest chemistry with ...?
Notwithstanding the fact that he's never had anything but good screen chemistry with any actress... the answer, of course, is:
Shirley Henderson.
What's so oddly charming about this is that she is not what I'd call a "looker" while Rufus is ravishingly handsome. They're no Brangelina (thank god for that) and yet they have the most remarkable chemistry whenever they're paired together onscreen. That breaks the rules, because isn't it absolutely taken for granted that a gorgeous man must be paired with a gorgeous woman?
And just by the way, wasn't Rufus (and Shirley) simply fantastic in Taming of the Shrew?