If budget isn't an issue, k20 would yield the best power/mpg's. K24 would yield the best torque, and still get decent mpg's.

If that's too baller for you, H22A's are pretty damn cheap considering the 200hp/160tq they make, but you'll need aftermarket mounts and axles to fit it into your car, bringing the cost up a little.

And if you just want ho-hum... if you're considering the LS motor, why not get a b20? hmotorsonline.com sells them for like $800 and you get the power of an LS with a healthy bump in torque. Definitely get the 99-00 version though... higher compression compared to the stupidly low 8.8 of the pre-99 version.