The main reason I think it's a better fit is because the characters in Phineas and Ferb very rarely leave their city. Them going on vacation fits as the reason why they're in WS, but it's kind of weird because you don't see them out of their natural environment (Danville) that much. Sure, they go to Atlantis, and there's an episode where they travel the world, but...those are outliers. Each episode is formulaic, for the most part. This is coming from someone who adores the show and has seen every episode multiple times.
Ducktales, on the other hand, has a "world travel/adventure" theme. It makes more sense for Scrooge & Co. to be in Mexico looking for a lost artifact than for Phineas and Ferb to be in Mexico on vacation even though you just saw them on vacation in China.
And for the whole "Phineas and Ferb is a human world" thing, P&F also has an anthropomorphic animal crime agency. I don't think the ducks in WS will feel too out of place, depending on how they theme it.
He does love Ducktales, though. Has the PS3 game, DVDs, and whatever merch we can find for a reasonable price. I do enjoy the writing for the current iteration. It's really well done and fits the theme of the show, although I do suppose Ducktales is a better fit thematically.
