Depends on your budget and plans. If you plan on switching to mod at some point don't skimp on the esc. If you want something to run club races and cheap The Speed Passion Citrix is a cheap choice that can handle a 9.5 turn.
Mod Touring Car
Wheeler and Mod Buggy
Check with your local club that you plan to race at. They will guide you with the rules they run by.
I have a 17.5 spec setup with an Tekin RS ESC set in lock out (blinky) mode. I can run in open class if I program my ESC to run boost. We use a locked timing motor for spec that the LHS sells just for this class.