It's best to keep up with the latest designs every couple or seasons or so, but as others have said don't sweat it. Club racers seem to love the Trackstar, and the current ones that either say short stack or 1S get a good press.
If you're going to invest for a couple of seasons - and in 1S the motor when geared right is hardly getting much stress - then I would say you should look at the slightly costlier ones with a good brand name. Having said that you could get get two lower cost ones for the price of one brand name.
Pick one you like and race - getting your lines right will give more time than any motor. HTH
