Your choice of flashlight depends on what flashlight parameters are most important for YOU. For example, throw may be more important. Or, runtime may be more important. etc. etc!
However, as a quick guide:
The T3 is shorter, lighter, and less bulky than the FT-3C.
FT-3C is brighter, has greater throw, has slightly wider beam/spill light, and has considerably longer runtime than the T3.
T3 has black finish; FT-3C has clear chrome like finish.
T3 has regulated circuit; FT-3C is not regulated.
T3 can be dunked in water; FT-3C cannot (or should not) be dunked.