The "T" designation denotes the size of the bulb, nothing else. The size of the bulb doesn't have a lot to do with how "good" they are for corals.
But you can think of it that way, because T5 lamps are more efficient and put out more light in less space than T8s. In fact, T8 lamps put out so little light compared to T5s, PC, or VHO that it's difficult to fit enough of them over most aquariums to form an effective blanket of light.
If you are keeping or are planning on keeping corals, there are only two technologies you should be looking at, T5 and Halide.
Does that help answer your question?