It's difficult. I bought the n800 just before the n810 came out. At first I thought I'd like the 810 better but I'm not sure anymore.

The n800:
is a lot cheaper
has 2 full sd slots
has fm radio
boots faster ?
has easy to reach buttons (no need to slide)

but:
no gps
no hardware kb

I think I'd still choose the n800 but I'm not sure. I do know I don't regret buying one.