How big is this? For mini-Sumo, tracks are fine. For two-foot-sized robots, tracks are a PITA. On the other hand, four-wheel steering is also a PITA; two-wheel steering is much easier.
The Dagu Wild Thumper comes in four-wheel and six-wheel versions, and uses "tank steering" with wheels -- it breaks the wheels on the side it wants to turn towards. It "works" as long as the surface you're driving on isn't too grabby. Dirt is great; anti-skid carpet, not so much.