Instead of paraphrasing I will just give you a link that explains it all......
LINKAluminum type rods last the longest BUT can get a build up of scaling which can make them difficult to remove.
Magnesium type rods deteriorate quicker BUT can react to microbes in water and cause a sulfur like smell
Suburban Brand have a steel tank that is glass-lined and therefore need an anode rod to help keep tank wall from deteriorating
Atwood Brand use an aluminum alloy tank so no anode rod needed
Your water heater IS grounded otherwise the propane & electric systems would not function. Further grounding of tank will not stop the 'galvanic' action going on inside tank between tank wall and the water
