I'd say given your size, I'd agree with The Saint. A large, full-size, full stock gun would probably look kind of small in your hand anyway (caveat being the "built like a stick bug" thing). I'm only 6' tall and a full size M16 feels great for me. It should be even more suitable for you. With your size, a full stock gun is a better choice as you can use a large battery. An M14 is a good choice for your size too, although the M14 is not for everyone.
If you plan on playing indoors, a full stock MP5, UMP, M4, or G36C would make a good choice. It would still be big enough for you to feel comfortable yet compact enough to move around in tighter quarters.