If you are in the following California air quality managment districts: SCAQMD, BAAQMD, YSAQMD, SJVAPCD then the ONLY water heater which can legally be sold or installed is the ULTRA low nox. They run about $100 more than a regular lo-nox.
Stay away from Whirlpool ( google for class action lawsuit, etc.). Tops are Bradford White, Rheem. GE is made by Rheem.