i4 - B18, the K20 is better, but the B18 brought mad power for its time and size.
i5 - Probably some audi shit
i6 - 2JZ hands down
v6 - Buick 3800 S/C. Not the BEST performance, but reliability is unreal.
v8 - LSx
v10 - they're all too expensive and stupid.
v12 - see above