If you're coming as a tourist it really depends on what you're hoping to find. Central Pattaya is very much a tourist destination although its suburbs, Jomtien, Naklua, and the Dark Side (ie east of Sukhumvit) are mainly populated by expats.
Phuket is great for tourists too - try Patong rather than some of the quieter towns unless you're looking for a quiet family holiday. If you're interested in beaches, then Phuket is by far the nicer. If you want "night life" Pattaya is probably better. It's horses for courses. I don't think that one place is really "better" than another. It depends on what you're looking for.