New Life Spectrum is very good and matches the Oscar's natural diet well. In descending order of top quality would be: Omega One, Dainichi, Hikari Bio-Gold, and Hikari Gold. I'll attach a very interesting article on feeding oscars that breaks their diet down and what you should use
Personally, I don't like Hikari because most of their cichlid foods have a lot of corn. I prefer Omega One and New Life Spectrum. New Life Spectrum has several variants with pellet sizes appropriate for Oscars.