3 days for sure. I just got back and did 4 days (2 at each park) which was perfect - although I didn't do everything, I did most of the main attractions on the first day at each park and that left the second day at each park for a more relaxed wander, doing the smaller attractions and taking in the atmosphere and entertainment. You'll have a great time with 2 days, but 3 would be much better. Bear in mind that at the moment you can't park hop - you can only buy 1-park 1-day tickets. Hopefully that will change by the time you go!