Pendants will have a nice finished exterior suitable to be used on an open top tank and mounted to the ceiling via a chain or something. The reflector will be just the metal reflector and socket, no finished housing, generally used inside of a canopy.
So, both are good for their applications, are you going to run a canopy? If so use the plain ole reflectors (usually much cheaper than the pendants). If you're running open top, use the pendants.
