I just replaced the hot water heater in our home. I bought a unit with a 6 year warranty and upgraded it by replacing the cheap plastic drain valve with a brass one. I also swapped out the aluminum anode rod for a magnesium rod. I plan on replacing it again in 4-5 years. An impact wrench makes it easy to get the old rod out by the way.
Old Biscuit is spot on with his information. Everywhere I read said that magnesium was healthier than aluminum. Here's a
link for a site that has lots of info about anode rods and water heaters for the home.