I bought the 16Gb WiFi model and I am happy with it. Of course I have to be smarter in the way I sync my media because of the relatively low space, but I am using smart playlists to sync music and photos. It works very well and I manage to have 5Gb free! Air Video is also a great app that I use to stream movies from my Mac Pro to my iPad without needing to copy the files over to the iPad.
I bought a 16gb 3G. I don't watch movies or TV shows on my iPad; that's what the TV is for. For me, it's a book reader, a photo browsing device, a web browser. And as a result, 16gb is more than enough.