Objectively, I'd have to go with Dolphy, in spite of not being allpwed to. The cat had the emotional AND technical depth to meet Mingus head-on (and then some) at every possible level (and then some). I think Mingus knew it too.
Subjectively, I'd still choose Dolphy, but I got a thing for Clifford Jordan and Charles McPherson too. Booker is like the bark on a tree - he's always going to be there being what he is, easy to take for granted, easy to get too excited about, but still essential. George Adams is the guy who was w/Mingus during my active awareness of jazz, him and Ricky Ford, and he made a deep impression on me, especially on those CHANGES albums, so I can't slight him.
Hell, Mingus didn't work with any bums. They're all good!