[Tom Bottiglieri]

I think instead of asking "should we use treads or wheels?", you should first establish what you want your end functions to be.
Ask questions like:
"How important is turning on a dime?"
"How much weight will we have?"
"What do we have the resources to build succesfully?"
"Would we rather be powerful or agile?"

After you set up what you want your robot to do, your design choice will pretty much fall into place. You can use some tools such as a decision matrix to further investigate what the best design for your application is.

Remember, let function drive design, not the other way around.