Basics: T5 is a long tube like your old fashioned shop lights, only much smaller diameter, and many more lumens per watt. PCF is a floecent bulb that double-backs on it self, with the socket at only one end.
The major advantage of T5 is the parabolic reflectors available for them. These massively increase the efficiency of the light. Without the parabolic reflectors it's a tossup between the two. If you're building your own hood, PC
doesn't require as much measuring, because there is only one socket per bulb instead of one on each end.