The P3 is better than the P2. I did a side by side when I was buying a t/t. The P3 has a better arm, a glass platter and a more expensive motor (I believe).
Not that the P2 is bad, it bettered the Projects I heard around the £200-250 range quite comfortably. P3 is worth every penny extra, assuming you can stretch the budget to it, but it's £300 without cartridge. If you've got a strict budget, you won't go wrong with a P2 or a NAD 533.
If you've put a £200 limit on it, go NAD as it's got a nice Goldring cartidge thrown in, as good as the ortofon OM carts that come with the Project Debuts/1/Expressions.