Most of us have to choose between gas and electric when it comes to our kitchen range. There are pros and cons to each -- neither is a perfect cooking system.
Gas is better for stovetop cooking, because it's a far more controllable heat source. Gas burners heat up faster and cool down faster than electric ones, and temperature gradations are more precise. Electric is a less efficient source for the stove. However, it's the more efficient heat source for the oven, and it's easier to incorporate a self-cleaning oven feature in an electric range.
Dual-fuel ranges mean you don't have to choose between gas and electric. New ones come with a gas stovetop, which is the preferable cooking method when using pots and pans, and an electric range for a more efficient, self-cleaning oven. It may be kind of a pain to install either a gas line or a proper electrical outlet if you don't already have both in your range space. If you do, though, you just hook it up like any other range.
While we're on the topic, another big plus in new ranges is induction cooking. Induction burners heat up faster and are more efficient than both gas and regular electric.
Efficiency is huge right now not only because of power bills, but also due to increased concern about energy availability. Along these lines, environmentally friendly kitchen design is really taking off.