I hate playing lefties more then anything, so a lefty slice just totally screws me up.
Other than that, if it's coming from a righty, I can't think of a shot that really bothers me. I have good wheels and more then enough power to hit through a lot of people. If I had to pick a shot, it'd be anyone that sits lower then my thighs. I like taking higher bouncing shots to really rip with!