Well since you didn't say what mk of supra you want I'm going to asume you mean the mk 4 (the newest make and what I drive).
For one, the different engines are the,
2JZGE
2JZGTE-ct28 (japanese)
2JZGTE-ct12b (american)
The engines are practically all the same except;
The 2JZGE is nonturboed.
The 2JZGTE-ct28 has 2 ceramic wheeled turboes, which can't be worked as hard as steel wheeled turboes.
And the 2JZGTE-ct12b has 2 steel wheel turboes (so the car can be driven harder than the japanese model), larger dump pipes than the 2JZGTE-ct28, aswell as larger injectors and a number of smaller differences that make it better than the japanese model. Its also .4 seconds faster than the japanese model 0-60mph, taking only 5.3 seconds.
Other than that they are really the same engines.
So the american model has the best engine. The 2JZ engine is also very easy to modify.
mkiv.supras.org.nz