I'd probably follow Brock's footsteps and be a Breeder, particularly of Eevees.
Or I could be an Ace Trainer, with a Photojournalist job on the side. (Like I would work for the Sinnoh Newspaper or something)
I think being a Gym Leader would be boring, because you have to wait for trainers to come along, and I am much better with a mixed Pokemon team anyway.
So I've narrowed it to Breeder and Ace Trainer/Photojournalist. How about I just be both? :p A trainer with more than 6 Pokemon at a time and has a camera around his neck to capture a picture of anything, whether it be nature or a Pokemon battle.