Did you try a search here? Many people have had troubles with the Whirlpool...I would avoid it. The most recommendations come from Bradford-White or Rheem. There is usually nothing different between the WH on the length of the warranty...you are paying for an insurance policy, not better quality. Some of the warranties may not get the full effect unless you have it installed by a professional.
Depending on where you live, the codes may have changed, and you would need additional work done to let a new WH comply. Where I live, all new/replacement WH are required to be installed with a tempering valve, which can be a little daunting if you've never installed one before, and can add several hundred to the installation price, not some much for the parts, but the time to install it.
It really depends on your usage, but energy costs are not likely to go down for any long time, so increased efficiency helps anywhere you can get it. WH is probably the biggest energy use next to the refrigerator and system heating. If you look at your gas bill in the summer, depending on what else is fed from gas, you can probably figure that 70-80% of the costs are gas. In the example you gave, a 5% difference in efficiency based on the lower one is nearly a 10% increase in costs.