Energy star qualification, as I remember it, requires a minimum of a 10% improvement over the normal efficiency. You'd want to look at the actual stated efficiency to see if one stood ahead of the other. To obtain that efficiency, it will likely have some sort of automated damper to prevent a chimney effect when the burner is off from cooling the water back off. Bradford White is generally only sold to pros, but sometimes you can buy them yourself (but often at a higher price). Not sure who actually makes the Powerflex. As there are really only a few manufacturers of WH in the US, but lots of brand names, if it is part of the group that makes the Whirlpool, and others, I'd go the extra effort and buy the BW. BW also has some neat add-ons for some models such as a leak alarm, auto water shutoff on leak, and a really simple to install tempering valve with a full hot tap off (for things like the dishwasher, which works better at a higher temp). They also have a setback system, which is more handy if you might only be there on say weekends, but gives you more accurate and easily adjustable setting of the water temp. Any of these can be added on, if the gas valve is compatible - they essentially bolt on and plug in, making it quite convenient. One way to make a WH look bigger, is to run it hotter, but for safety, put a tempering valve on the output. It increases the standby losses (higher Delta-T), but not a huge amount.