I think Palpitoad's probably has more experience in battling. It's been guarding that lake for who knows how long, debuted with a pretty strong moveset, and it won a few more battles for Ash. On the other hand, Palpitoad lost to Oshawott, who lost to Boldore (as a Roggenrola), though, Roggenrola used the area around it to make Oshawott KO itself.
So I'd say Palpitoad is stronger in terms of brute force and power, but Boldore is craftier and would be harder to beat without Ash's guidance.
Sprites from Serebii.net
sees two options that shouldn't be there.
Obviously Palpitoad would win in a head on battle because of the type advantage, but even in a test of strenth I would think Palpitoad is stronger