My iPad history:
iPad 1 - 16GB WiFi
iPad 2 - 32GB 3G
iPad 3 - 64GB LTE
For me there is a growing need for more space. I don't load movies/games/music on my iPad but, quality dictionary/reference apps, video podcasts, GarageBand, pdf's and photos occupy a lot of space. When iPad gets full performance starts to deteriorate.
It really depends on how you use your iPad. My advice is to try 32GB, which i think is the best for most people for a few weeks and, if necessary, exchange for smaller or bigger capacity iPad.