There's no reason whatsover to wait for the entire series to be published before reading A Song of Ice and Fire. You see, every new release will give you a reason to re-read the entire series - what could be better?
I personally think that A Song of Ice and Fire is superior to The Wheel of Time. The characters seem much more real, and I care much more for them, whereas a lot of characters in WoT simply annoyed me. The first few books of WoT were interesting enough, but I think the story really started to drag around book 6-7. I once read book 1-6 in the series, then I gave up. Later I decided to give it another go, and this time got as far as the middle of book 7. The story just seems to die down at this point, don't really know why. I have great respect for the diverse world Jordan has managed to create, the various people that inhabits it(I especially like the Tuath'an - in a way I think that "The Tinker and the sword" is the saddest chapter in the books), and the books certainly has that epic feel to them. In the end I think it was the lack of really interesting characters that bothered me and made me lose interest. I simply didn't care that much about what happened to Rand, Egwene and Mat anymore, whereas I never think I will lose interest in the fates of Tyrion, Jon and Arya.