If you can, do both. However, as far as the slippery issue, that will be good for you to learn to deal with; what if the drunkard spilled his beer? It's also good because you're training to do holds that are really hard when they're slippery. Imagine how much easier it will be when they're dry. But if you can, train in both. You'll get a different experience from each one that you wont get from the other.