{With Bill’s, I stick to canon: eevee and all of its evolutions, with a preference for flareon, jolteon, and vaporeon in particular for the latter. He’s still fond of the pokémon on his team as well (kadabra and venusaur and so forth), but really, eevee and its evolutions have always taken his top spots.
As for Lanette, she’s got a soft spot for anything that’s cute, especially any and all feline pokémon (of which delcatty is probably her favorite). She’s also very fond of clefairy, which are basically the magic spacecats of the Pokémon world anyway … and also because she’s gained a new appreciation for them thanks to the whole Clefairy Incident. (She thinks they’re hilarious now; Bill decidedly does not.)}
The Pokédex According to Bill 