A simple animation describing how a heat pump water heater works
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We are working with A.O. Smith, GE and Stiebel Eltron on a Building America task to drive the uptake of HPWH technology, so I'm in no position to pick a favorite brand.
You might be interested in Alex Wilson's take on the technology...and he offers some guidance.
As Alex points out, you might not have any choice in the matter after 2015...."New federal regulations that are due to kick in on April 16, 2015, will require that electric water heaters larger than 55 gallons have energy factors close to 2.0. .....—a performance level that can only be achieved with heat pump technology.
The energy factor requirements for smaller water heaters—up to 55 gallons in size—are also rising in April 2015, but will remain below 1.0 and will be achievable with a very-well-insulated electric-resistance water heater."
Nevertheless -- Caveat Emptor
Not sure if you are being sarcastic, but a serious answer would be that GE is selling their completely "made in USA" heat pump water heater with a 10 year warranty on both parts and labor....And the DOE/Building America program supports them with quite a bit of research....utilities all over the country are offering rebates, and heaven knows they aren't into risk....I will say, however, that HPWH's do carry a lot of historical baggage with them -- having been through a couple cycles of development and deployment with less than satisfactory results..so we are seeing some pushback from plumbers with long memories. Constructors tend to go slow and hold on to war stories forever. To wit builders that still use "tar paper" in lieu of non-wovens.
Here's a link to a website with lots of information on the topic of heat pump water heaters -- you can decide for yourself....