you can run either 14 guage or 12 guage. With 14 guage wire, you absolutly can only use a 15 amp breaker. With 12 guage, you can use either 15 amp or 20 amp breakers but why limit yourself with 15 amp and 14 guage. Run your 12 guage wire, use a 20 amp breaker, put in a double box for 2 duplex receptacles side by side for all the stuff you will need to plug in. run another box on the opposite side of the stud wall cavity for the cable run and for a phone line run which would be needed for satelite tv conversion. run a separate 12 guage/20 amp circuit to the garage as motors and florescent lights cause the most interference to tvs, computers, etc.