I like to use an ultra low watt density element when I replace water heater elements.
This # 02953 4500 watt / 240 volt Ripple Foldback Lime Life element made by Camco Mfg. Inc. has a wattage density of only 50 watts per square inch and offers a substantially insreased service life even in an area with heavy lime properties in the water. The nickel and chromium incoloy elements are claimed to even stand up to being dry fired even though I have never personally verified this claim.
Click here for the manufacturers web page
Note: They also sell a 5500 watt element which I do not recommend. Many water heaters are not designed for the additional 1000 watt load. This product was designed for big box stores where they may claim bigger is better.