I would start with the olympic. Remember, that 1/2 marathon you'll be running is AFTER a 1.2 mile swim and a 56 mile bike ride in a HIM. There's your pacing, nutrition, and transitions to worry about as well as making the distances. I think you'll enjoy your first tri a lot more if you know you can do the distances instead of a race where you may be pushing your limits. It'll be one less big thing to concentrate on.