if you go with the d16z6, pretty much the only way you'll make significant power is with a turbo or nitrous. The ceiling, in terms of power, will be in the 160-220 range unless you rebuild the motor to accept more punishment. The D-series option has a lower initial cost, but you can only go so far before you run out of ways to improve power.

A B16A or B18B cost a little more, but have a much higher power potential. Keep in mind, a well-tuned, turbo'd D16z6 will make loads more power than a stock (or moderately modified) B-series... but turbo/nitrous that B-series motor, and you'll blow the D out of the water. Either route has its advantages. What, exactly, is your power/performance goal? Figure that out first, and it will be easier to tell where to go.