the best motors that i've either raced myself or seen run and liked:
(not in any particular order)
Mugen Ninja .21
OS V-spec .21
Novarossi 21-4
Novarossi Toro Nero
Axe Rossi Mamba X1
Dynamite platinum 21
any GRPs
Reedy 121 VR
You can't go wrong with any of these motors