I have the bold 9700 and love it! Fast and small. It is smaller than my curve was. I'm on rogers as well and works great. This is my 5th BB and the best I have had.

But here are some of the biggest differences:

The Bold is larger than the other two, and it's faster as it runs on Rogers 3G network, and the other two only run on EDGE.

The 8900 has a higher resolution camera than the other two.

The 8520 doesn't have a flash for the camera. It's a more "entry level" device. But it is the newest, so it has the little chicklet-like optical trackpad rather than the trackball that the other two has, so it will never have the problem of dust or gunk getting into the device that way.

My twenty year old daughter has the 8900 and is very happy with it. My seventeen year old son has the 8520 and is very happy with that. You should really pop down to a Rogers store and get your hands on all three before you make a final decision.

Good luck!

http://na.blackberry.com/eng/devices/compare/

Go here to compare BB phones side by side

i have the tour 9630, it is my first one and I love it. Full qwerty key bored, all I.M. programs and all that are already there on the phone. Check it out. Though I have mine through Sprint idk what wireless company you have but if they carry the tour check it out.