Larger burners heat water faster. The warranty on heaters can be extended with kits that include an extra anode rod. Anode rods are made from magnesium or aluminum. They are made to self destruct inside the heater. Without anode rods, water heater tanks would fail within a year or less.
Water expands as it is heated.
This can stress the tank. It is best to install an expansion tank at the same time you install a new heater. The expansion tank contains pressurized air and a rubber bladder. When the hot water expands, it pushes into the tank. As it cools, the bladder pushes the water back into the piping system.