What are the best sources of XP after the Elite Four in BW2?

In Pokémon Black 2 and Pokémon White 2, what are the best sources of XP that are available after defeating the Elite Four?

Defeating the Elite Four again is the traditional post-game XP source, and Route 15 has some high-level Pokémon, but where else is good?

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1 Answer

Black Tower and White Treehollow. As Krazer said in the comment, there are trainers who use Chansey and Blissey in the White Treehollow, so there's more experience there.

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