Well for what you want to do the chain drives would probably work. They're not as tough as four motors. I would use four motors. The chain drive sounds cheaper but if you buy smaller motor/gearboxes you can eliminate two pillowboxes, an axle, four sprockets, two chains, and a lot of adjusting. It leaves more room inside. I kinda like RC car steering though. It's more accurate on the long straight runs. One of the problems of skid steering is getting precisely the angle you want. Some guys put a heading hold gyro in the circuit and let the gyro manage the skid steering. The RC car style steering isn't as maneuverable but it will carve a turn nicer. Maybe a combination of the two would be best by steering the front motor mounts with a servo and y- connect it to the ail channel external to the dual ESC, installed after a heading hold gyro. When you want skid steering it would still be available. (That smoke is my lightbulb going off). Hey I like that, I might use that on my next project. Well I'm no expert in robots, but I stayed at a Holiday Inn last night I did make a few RC lawnmowers which you can see at http://www.hoverbatics.com/200MPH
-Tom
-Tom