For me three things.
Precision of Touch- But I should talk. I have Fat Finger Syndrome
Battery Life-I want a unit that has 10+ hours in reality
Quality variance - Looking at the board, this is an obvious
Portability and view: My Firmware is solid and I can now browse,watch movies, read or listen with ease. I can even listen and read while my battery drains faster.
Show-off power. I do not care where I use it, I always get comments and questions
Not an IPad and it fits in my pocket. Without a case of course. But bigger than a PMP and more portable than an IPAD.