Out of the Mtronics range there is only one controller that offers proportional Fwd and Bck and instant reverse and that is the Tio Marine range I believe:

http://www.mtroniks.net/products.asp/Su ... 65/tio.htm

Note though, those ratings appear to be peak and not constant.

I would go with Electronize, I don't know why so few people use them. They are seriously hardy (more so than most other controllers, the 15a model has a 40a peak rating and 270a burst!), apparently can be upgraded easily and come with a cover, so you don't have an exposed PCB in your robot. They're also one of the cheapest.