Winterspring for the Winter Olympics would be beautiful, but I would hate to see it after the events were over -- all that pristine snow trampled with footprints, the discarded steins and pony kegs piled up beneath the pine trees, the holes in the ice where Tauren figure skaters fell through...
So for practicality, I would say the Barrens. There's a variety of terrain with the savannah, oases, mountains, Wailing Caverns, the Razorfen instances, river, and sea. And, Fray Island is just offshore to host boxing, wrestling, fencing, judo, taekwondo, rexkwondo, and unarmed tuxedo dueling.
An additional benefit to the Barrens is that, with all the spectators running around, someone is sure to finally stumble upon Mankirk's wife.