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Are we speaking about RAM or flash storage here? The RAM in the iPad is actually always the same: 512 MB DDR2 (1066 MHz), although that's not an advertised spec and nobody should really cares about this (except app developers).
The iPad 2 has either 16 GB, 32 GB and 64 GB of flash memory. I have an iPad*2 with 32 GB and that's enough for me. If you aren't going to put gigantic files, videos, or a lot of music on it, you'll probably be fine with 32 GB too. Take note that iOS itself is taking about 5,5 GB of that storage, and apps take storage too (especially games). Unless you use your iPad very lightly, like you're just browsing the web and using a few apps, the 16 GB model will probably feel a bit cramped.