A week ago I said 64. Now I'm thinking possibly of 32, mainly because iOS 7 is letting me stream music and videos without downloading them. The main thing I hated about using iTunes' cloud service was the requirement to download songs before playing them. But with this, I may not need the extra 32GB as much. I'm scooting by on 16GB with the occasional need to delete something and a complete lack of games on the thing.
So right now I'm leaning 32 but considering 64. Had it been 64 and 128 at these price points, I probably would've been totally on 64 at $299.