Personally I believe the question is 32gb or 64gb. 16gb is very light and there was no way it would work for me. I got the 64gb.
That said, what is your usage plan? It is important to know what you will do with the device to decide.
If money is tight, get the most memory you can afford. You probably won't be able to trade up later if you run out of space.
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Your main question is where do you envision using it?
If you will be mainly using it at home then 16 with streaming apps like airvideo and zumocast will be fine.
If you travel a lot then the larger size will definitely be needed.