1 or 3 sets?

Does it really make a difference, 1 or 3 sets?

what are you trying to achieve, and how many reps are you doing? Give us some specifics

I am looking to build functional strength, and to decrease my bodyfat % from 8% to 5%. I do bodyweight and every once in a while i use dumbbells. I try to keep to sets of 5, and sets of 10, but I'm in JROTC in my high school and that naturally gives me a lot of practice with high rep. single sets with 30+ at a time (for example, pushups, and situps). Pullups I can only go up to about 5, and chinups only up to about 10.

so, is it better to do 1 set or 3 sets?

I'd reccomend two sets, a la PTP. there are several threads on power to the people here - check them out.

since you mention "funcitonal" strength, remember to do the big compound exercises - bench, squat, deads, etc. pullups are great too.