the bull shark.
on a side note, your GSP's will do much better if you acclimate them to a sea environment over a few months, you will notice their color will brighten greatly, their bellys will get completly white intead of that dark gray/black spotted color that you have no doubt seen before. that wont work for your Oscar but the gsp's will thank you in the long run and be much healthier and less prone to illness.
today i went to my LFS and pre-ordered a snowflake moray eel, and a niger triggerfish. should be having them in a week or so. just long enough for me to get my tank outside up and running (albeit not cycled).
im going to give the reef tank idea a try...