I would mostly agree with what people here are saying, but I would also suggest looking into the Hobbywing Xerun ESC. It runs sensored and sensorless motors, has the optional "boost" and "turbo" functions if you need it, and costs less than other ESCs in its class. Some people will knock it because of its low price, but be sure to look for yourself at some of the feedback on the forums. I have used many types of brushless systems, Novak, Tekin, LRP and Castle just to name a few, and I believe Hobbywing makes one of the best products in the business.

I would also like to add that Hobbywing's sensorless ESCs(EZrun) are very smooth and do not hesitate or cog at all when set up properly.