I have a Rheem Marathon WH, which was installed when I built the house. It's 8 years old now. It's plastic and the tank has a lifetime warranty (for what that's worth) and the plastic, of course, will never rust out. But you have metal fittings passing through the double-wall plastic tank and the possibility of those interfaces leaking, especially over many years, is certainly a potential problem and I think some of the pros on this forum will attest to those potential problems. Nonethess, mine has performed flawlessly and I would certainly recommend the Marathon WH. The heating elements are specific to the Marathon WH and you cannot use off-the-shelf heating elements with it, so when I bought the WH, I also bought a spare set of heating elements (the upper and lower are different from each other) that I have ready for when either of the originals burn out. I have a 50 gallon unit, and the Marathon WH is $500 +/- more expensive than a generic electric WH.