T5 and Power Compacts are roughly equivalent as far as power consumption vs light output, but are more expensive in terms of fixtures and bulbs. T8 are a bit less efficient but the fixtures and bulbs are less expensive. I'd recommend figuring out how much light you want over the aquarium, and then buying the fixture that gets you closest to your goals at the best price.
Any particular reason for the limit on plants? If you're going lightly planted, I wouldn't go more than about 1-1.5 WPG just to help avoid algae issues.