Most of the commercial examples of Pumpkin Ales are based off Ambers. Other less prominant commercial examples are based off Browns, Porters, or Stouts.
If you want to make a Pumpkin Beer that tastes like liquid Pumpkin Pie, base it off an Amber recipe.
I made a Pumpkin Stout this year that is really good, but the body of the beer is more defined by the Stout properties than the pumpkin spices, and I put a ton of pumpkin spices in there, along with 56 oz of pumpkin meat in the mash. The same would go for Porter-based, the Porter properties are going to dominate. Brown would be somewhere in the middle. I'd go amber if you want to really taste the Pumpkin and Spices.