Should I go with AT&T, Verizon, or Sprint?

I'm almost 16 years old, and not only is one of my New Year's Resolutions to be more mature, but I am also going to be 18 in a couple of years. My dad pays for six "unlimited-everything" phones, so I especially would like to help him out a bit.

Back to my original question, which phone carrier should I go with: AT&T, Verizon, or Sprint? Also, I plan on getting an iPhone 5. Price isn't really a problem, but please include both a higher-priced and lower-priced answer. Thank you!