hshah8970 gave an excellent explanation, while dlhylton ... well, you have much to learn.
The conductive action that turns a bipolar transistor "on" is the presence of minority charge carriers in the base region, which are drawn in by the base-emitter potential due to the emitter's high doping concentration. (The emitter "emits" charge carriers into the base, which are mostly swept up by the collector before they have time to recombine in the base). In an NPN transistor, the charge carriers happen to be electrons which have high "mobility" (i.e., they move fast) while the charge carriers in PNP transistors are holes, which have lower mobility. So, for a given cost, NPN transistors simply conduct more than PNP's.