If you want to turbo it ----->sc300
If you want to keep it N/A---------sc400

Its simple!

 

I'm biased towards the 400, but neither is "better". As others have said, the main reason why the 300 is popular is because it's more closely related to the Supras, so it has more aftermarket support. I personally like the 1UZ more than the 2JZ engines, and if you look into its development, you'll realize it has just as much potential as the 2JZ. It all really depends on how deep your pockets are.

I'm a V8 person, though. I hate driving a car that has anything less than a V8, so take my opinion with a grain of salt.