I picked Ptolus because to me, of these five, it's the best product in quality and overall scope.
I also think that this poll is scewed because people can vote multiple times and the results will be biased because of it. And I think because people are voting for what their favorite product on the list is, and not what would be classified as "best", which are two very different things.
if I voted what my favorite product on the list is, I'd pick Eberron hands down because Eberron as a world is so much cooler and better than Ptolus... but this poll asks what is the single 'best' product from 3.x era, and that's a no contest... Ptolus should have won this poll already because no other product touches what Ptolus strives to achieve, with as much detail and as colorful and as much time as was put into the product.
And for the value of the product it is well worth it.
I'm just curious as to how a adventure series like Pathfinder can be voted upon at all, let alone make it this far. Is the entire series even out yet? If not, then it shouldn't be an option at all... and if we are talking about one adventure, then it's a no brainer that it's not the best overall product of the 3.x era.
Best = Quality and Scope of achievement, not Favorite.