Most 14 year olds I know like IOA better than USO. Even my husband and I love IOA! More exciting at IOA. USO is too laid back (something my Grandmother would like). So, I agree with USO2003:
Thrill seeker would go to IOA
Laid back people would go to USF
Go to Universals website with your 14 year old and have him look at the attractions at both parks & let him decide.
Have a great time!