Can't tell you which one to buy, you have to make that decision!
I had a 9000 and sent it back after 2 weeks.
My reasons were:
I found it very big and heavy after my previous Pearl.
The software was very buggy, hopefully that's improved now though.
I wasn't mad on the keyboard, the keys are raised in an L shape and I found I was pressing the keys off center.
I then went for a Nokia E71, shame on me, 10/10 for the hardware, 0/10 for the software, this went back very shortly after!
I now have the 8900 and for me, the software, size, weight, etc make it perfect.
I use it as my only device, Voice and Data, maybe if it was data only i would prefer the extra size and speed that the 9000 has.
I would say that you have to go and hold them both and see which one you fall in love with!
BlackBerry Bold2 9700 / 220.127.116.118 / BESx
Blackberry Playbook 32gb WiFi / 18.104.22.1680