I have both...I started with the Party and cooked a couple of contests on just the Party, it takes a little more touch and good timing but is not difficult. The big downside is your limited in the amount of meat you can cook (I always did 2 butts, 1 brisket, 3 racks of ribs and 12 chicken thighs).
I also agree with the guys above the Fatboy is much more cooker, mjl covered the issues very well. I would recommend you go look at them if you haven't done so already, it will make your decision easy when you see them in person. IMHO the Fatboy is the way to go...especially if your going to compete, I would be $1400 wealthier if I had bought the Fatboy first
but there's no way I'm giving up my Party now
Good luck, you will love it no matter which way you go. IF you have any other questions just fire away...