Three Words: Heat Pump Water Heaters. OK, four words.
We think all gas water heaters suck. They cause a lot of problems in Home Performance retrofits. That's our bias. That said, here are some products to consider. Please DO NOT buy a standard gas water heater, though, your odds are 50%+ it will backdraft after upgrades and you'll have to replace it. We hate those conversations, and hence gas water heaters... So check these out first.