Well, if you're talking motor for motor.... completly stock... I would have to say the SR20DET.

It's been around for a good while, it has made well over 500whp stock, and has been tried and true for years....

Granted the 4g63 has been around longer, an is strong until around 450-500whp... but that's about where it gives up on stock internals...

So my vote is the SR.