Well that depends on what you mean by memory.
Do you mean RAM? If so, then the more the better. To a certain extent, the more RAM you have, the faster your tablet will run.
Do you mean ROM? ROM is where apps are held, but it's different from the general tablet capacity in that it's exclusively for OS functionality and apps. The more the better. ROM cannot be expanded, so what you get is pretty much what you're stuck with.
Do you mean internal memory? Tablets have a limited amount of flash memory, typically between 16 and 64 GB, which is used to store media (movies, pictures, music) as well as some secondary parts of apps and certain apps which allow themselves to be installed to the SD card (or internal memory). Apps will take up a tiny fraction of this storage, so how much you pick is mostly based on how much media you want on it.
Android 2.2 allows some apps to be installed to the SD card. Android 2.3 allows more apps to be installed to the SD card, but not all of them. Some apps are stuck on ROM in order to function properly.