I'm exploring replacing my 18-year old AO Smith n-gas water heater, pre-emptively, before it causes trouble.
My first stop was the big box stores websites because of product/sales transparency - - oddly, the choices are not many.
I want 60-70 gallon size, and looked for 12-year warranty as an indicator of long-life, and I see only 1 model w/ 12-yr warranty @ 74 gallon from Lowe's, Sears & Home Despot - it is a Kenmore, for $850. A couple of 6-year warranty heaters were avaialble.
The 60 gallon size also had limited availability with 12-yr warranty.
Price difference between 6-yr and 12-year appears to be about 15%.
It seems manufacturers don't like to provide the 12-year warranty.