Like he said, it varies greatly on what class you want to run. There are ESC's specifically geared towards spec racing with extremely aggressive timing profiles that wouldn't work in modified racing. Other ESC's are geared towards modified racing, and then some work in both with some extra tuning equipment.
Motor depends on the track usually. I would scope out what people are running at your local track so you can get on track support on how to gear and setup the motors and ESC. Sometimes it's easier than coming on the internet and getting a multitude of different opinions and answers.
I personally like Team Orca (more info for you guys a little later) and LRP ESC's. LRP Offers the SPX for spec racing, and the SXX for modified. Orca will be offering ESC's that have tuning capabilities for both types of racing.
-Korey