I made this post in another thread; it's relevant here too.

I'm seeing this response a lot in relation to swerves. Say we go with a 118 style crab: All wheels steered together. Even with the type, the wheels don't suddenly make a 90 degree turn, or however much people assume. The robot will (assuming that it's driving) turn in an arc. The cleanness of this arc is a factor, but not enough to disqualify the design. Unless you're using some odd turning system, the wheels won't change direction faster than the robot can adjust.

For the sake of the point, now let's move to sets of 2. The front wheels are now steered separate of the rear. With a bit of programming, and a big red button, you now have the option of an AWD 4 wheel steering system or a standard crab. Say we drive each wheel independently, this opens up even MORE options. We can drive normal crab, normal crab with traction control (I mean, seriously, the Jaguars have built in current sensors! It's not THAT hard to do!), 4 wheel steering, 4 wheel steering with slip control, 4 wheel steering with Yaw control (see the Modern Subaru STI and Mitsubishi EVO for this), and more. Plus, at the hit of a button, we can move (in a short amount of time) from moving forward and steering to side strafing. We've got traction control already, so what's to stop you from using a gyro to even out the direction of the bot? Sure the trailer's going to weigh you down, but a bit of time spent in testing, and a decent programmer makes that problem nonexistent.

Personally, I don't see any other drive system that has more available to it than a 4 wheel crab with independent power. You can do almost ANY form of driving you need.