I've no idea what games you like, but I would say get the Wii then wait for a game you really really want on the Wii U before purchasing.
I like all the Nintendo's own games like:
Super Mario Galaxy
Wii Sports Resort
Zelda Twilight Princess
Zelda Skyward Sword (imo the best zelda since Ocarina of Time).
But if you fancy something a little more 'adult', Resident Evil 4 is one of the best experiences ever on Wii.
Metroid Prime 3: Corruption
(or the trilogy if you've got 100s of hours to spare) is also really good.
These games sold so many at launch, that now they're cheap as chips.