Wondering which flash to go with?

I own a nikon d90 and is loving it. However i would like a flash that has alot more control and i have 3 alternatives and i was wondering which would be better and why?
1.SB-600
2.SB-800
3.SB-900

Added (1). "control" i mean by how bright the light can go.

The SB-600 is a workhorse and has many features that allow good control. If I'm not mistaken, it's discontinued now and there are MANY used ones in the marketplace right now - can be had for a very good price. Nikon sold millions of these things.

When you say "a flash that has a lot more control", more control than what?

SB-700

It costs just a little more than the SB-600 and has the features of the SB-800 and SB-900, the ability to use the commander mode to adjust external flash units from the camera