Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
I think Drifloon and Ghastly are most likely to take over. Drifloon has a bit of sweeping potential, and Ghastly is pretty decent from what I've seen. But who knows what turn the metagame'll take.