Being a gas, I would look into getting a tankless. They come with a higher price and a fair amount more work to get them going. There is a decent chance the gas line won't be big enough. The cheapest and easiest would be to stay with the tanked water heater. Being a gas, I would consider hiring it done. Not saying you couldn't handle it, but there are several factors that make it a little more challenging. At work, we sell A.O. Smith. We've sold some Rheemes. Installed customer supplied ones from big box stores. They all seem to be close in quality. In this day and age of a throw away society, we always tell customers they should work great, but there's always the chance they may only last a month or one year.