Most name brand motors are going to be comparable, at least those in the $150+ range. For stock racing I run Trinity motors. The smoothness will be more noticeable with the quality of the ESC more than anything, I have grown to rely on HobbyWing myself, but any name brand $100+ will also perform well, the amount of money you spend will be based on what features a brand is offering, not that a particular brand is better, but if you want a current limiter, data logger, etc, then you'll have to pay more.