Hybrids are not the end of all of fuel efficiency. If your singular goal is to reduce the amount of gas you guzzle, then a hybrid is probably a good choice. That does not mean you will save money. The long term financial impact of owning a hybrid will cost you as much or more than standard gasoline cars. If you happen to be looking for the most fuel efficient car sold in the United States, the Toyota Prius (hybrid) is currently the reigning champion.
Only a few (more like one) electric car models can achieve average highway speeds. Those cars are rare, expensive and have long waiting lists for people who want a technological gimmick. Unlike hybrids, electric cars have to be plugged into the wall to recharge. Recharge periods can take hours at a time. You do spend less than 25 percent what you would on gas though.
There are actually a number of diesel vehicles that get better mileage than even the Toyota Prius, which is the most efficient car sold in the States. However, U.S. standards have kept diesels out of the market for years. They have also been stigmatized for being slow, smoggy and noisy. Much of this is no longer true. While diesels still lack the power of regular gasoline, the difference is no longer so obvious. Today, there are diesel engine cars that rival or get better fuel efficiency than regular cars.
Considering their size and weight, they don't get particularly great mileage. Nonetheless, their overall fuel efficiency is pretty good when compared with everything else.