Replace under warranty Bradford White or get a new Rheem water heater?
Talk to a different plumber. I don't trust anyone who suggests that I replace something that I could get for free under warranty! Even if it's not a good make you'll still get a new one and get another 4-5 years out of it, then you'll be free to buy the latest and greatest which will be more efficient. I'd get someone else to install a warranty replacement and save that money up.