I have both and haven't noticed a difference in performance, but I haven't actually done a proper comparison test either.
They do feel different, though. I find the flatter tops of the Universal bodies, combined with the full covers, a bit more comfortable than the MAFAC levers.
Here's the MAFAC-Universal combo on my Toortelboom:
I like MAFAC cantilevers and run them on several of my touring bikes and, because with those period-correctness is less of a consideration, I like to combine them with early Campagnolo Ergo levers. Besides their ability to shift vintage 5 and 6-speed transmissions, they are more comfortable, make braking 'from the hoods' easier, and there are no brake cables to get in the way when accessing a front bag.