I really felt that Platinum was the best of the three. The only version differences DP had were the available Pokemon, and after the big improvement RS made to separating versions, it just felt like a big step back. Also, not including a Battle Frontier after Emerald introduced it was a big letdown. But Platinum really remedied the issues DP faced, and since DP really had no reason to be separate in the first place, Platinum feels like the "right" game, because there's only one. The fact that it added a bit to the plot certainly doesn't hurt, either.