When 16" was the craze everyone wanted 17". When 17" was the craze everyone wanted 18". And so on...
Take a look at a race car's wheels... Weight is the key. If you want bling, go for the 22" with diamond studs like I saw at the Atlanta Auto Show yesterday. If you want racing wheels, go for the BBS LM-R. If you want looks, go for what you like.
Since you don't race cars for a living and 22" won't fit, go for what you like. I think the 18" look awesome on the Grey cars, the 19" look great on the convertible cars and the AW cars. Making decisions on what you want to order should not be based on what replies you get from a forum, it should be based on what excites you when you see it configured on bmwusa.com!
Name one person who can afford an M3 who says "Crap, I cannot afford the extra $1,200 for the 19", nor can I afford the extra $20 to replace a tire!"