I've seen both but was drunk both times so take that for what it's worth... I would say Kelly is more attractive, probably a couple years younger I'd guess, and she is easier on the wallet.
Kaka is pretty much down for whatever but I didn't find her hot enough to do anything with other than bbbj - and I'm partial to Asians. As for their skills, both are pretty wet and sloppy, can go for a while, Kelly will follow requests more and Kaka will shower with you and scrub your crotch like she's possessed.
If I had to choose it would be Kelly - on looks, price point, service & personality. Also location, as Richmond is far from me.