I prefer mine over my old 8320, and prefer using it to other peoples 8900's too.
Out of the 3, I would take the 8520.
Biggest downside is the screen resolution, which is good but could be better.
Lack of a flash is next on the downside, then 3G if such a connection bothers you.
All in all, one of the best out there, and if you cant get a 9700... the 8520 is the one