I have to go with Rougeau in this match. Neidhart simply never has done anything for me. Sure, he was the power guy of the Hart Foundation, but Bret was the worker. Neidhart is strong as an ox, but maybe as smart as one too, by his own admission. Neidhart was a role player, and a good one, but incredibly meh as a singles worker.
Rougeau played a great character in the mountie, and was able to capture IC title gold. He maybe better as a tag wrestler, but he certainly accomplished more in singles then the Anvil.