For the most part hard wheels have less traction, drift and slide more predictably, steer quicker from side to side and generally get less traction. Softer wheels (72a, 75a) are better for rough surfaces and lighter riders.

Now onto the wheel shape. Sideset wheels will slide the easiest and cone the easiest as well. Centerset will wear the least. Hard edges tend to provide greater amounts of traction while round edges provide less and slide more predictably.

That should help you chose some wheels based on those facts. I personally enjoy a slightly harder wheel (82a) so I can slide easily and comfortably yet still have plenty of traction when I need it. My current favorite is the Abec11 Flywheel in 83mm.