I also would like to know what size wheel would work the best on my robot.
We need much more info to even start making suggestions. This is like asking you "what size tires would work best on the truck I drive"?
Questions to help select wheels:
What is the robots size and weight?
What is the Maximum speed you want?
What kind of surface will it run on? Indoor smooth floors or outside on grass, rocks or hills?
Then there is the questions as to which motor/gearing you are using?
How you selected this?