PT's are best where you have quite a lot of light, e.g. photo-interruptor type scenarios, and can produce a direct logic-compatible output with just a pullup resistor. PDs are more for lower-light levels, and for measuring light levels, and usually need some kind of amplification.
for higher-speed data type things, the issue with a PT is that as data rates increase, you need to reduce the pullup resistor value, which increases the amount of light needed. For close-coupled links up to a few kbaud ( e.g. an isolated data link on a DMM), they are a nice cheap & simple solution, but once you need either higher speeds or longer distances, a PD+amplifier will be needed.
For low data rates over longer distances, TV IR remote receivers are good, as they have an integrated amplifier & data slicer, and output a digital signal.
IRDA receivers/transceivers can also be a nice solution, but are getting increasingly harder to find as irda is basically dead.