The race is on for the next generation of vehicle fuel in this country. Companies such as Clean Energy Fuels (Nasdaq: CLNE), General Electric (NYSE: GE), and Chesapeake Energy are pumping millions of dollars into building a natural-gas infrastructure that will navigate the country's highways. At the same time, AeroVironment (Nasdaq: AVAV), ChargePoint, and PlugShare are contributing to an ever-growing network of electric charging stations.

So which one will win, and which one is worth investing in? Let's look at the trends.

Power availability
One of the challenges of getting fuel to fueling stations is the infrastructure necessary to transport fuel. But both natural gas and electricity have advantages over oil in this factor. Electricity runs to probably every major building in the country, so anywhere a fueling station is needed, electricity is available. Natural gas lines also run all over the country, through neighborhoods and industrial parks alike, so a majority of locations where you may want to build a station would be easily accessible.

Electricity may be a little easier to hook up in some locations, but it isn't as if natural gas is going to have to build a new infrastructure to keep up. Slight advantage to the electric-vehicle highway on this one.

Vehicle adoption
If a fueling highway is going to be built, and worth investing in, you need vehicle adoption to take place. There are really two paths these fuel sources are taking to adoption, and both have had their struggles. Electric vehicles have focused on the passenger market, with mixed success, and natural gas is focusing on trucking and buses.

The passenger EV market has been full of disappointing sales for General Motors' Chevy Volt and Nissan's Leaf. But Tesla (Nasdaq: TSLA) has had a lot of success with its Roadster, and the Model S looks promising. Fellow Fool Alex Planes argues that when you put EV adoption into perspective, it's actually pretty impressive. The problem for EV adoption is, the financial commitment is harder to justify for the fuel savings involved.

Natural-gas fueling has focused on the trucking market, where dollars and cents are all that matters. If natural-gas fuel wasn't cheaper than diesel, it wouldn't fly. So when Clean Energy Fuels and Westport Innovations (Nasdaq: WPRT) work with their partners to expand natural-gas fuel usage, they have to offer a cost competitive product, not a tree-hugging story. This is why natural gas gets the advantage for vehicle adoption. It's an easier transition to make for owners, and the cost savings are easier to identify.

Range anxiety
If there's been one major knock on electric vehicles, it's range anxiety. Natural-gas vehicles eliminate that worry altogether, but EVs may be catching up.

Oregon opened the first stretch of the West Coast "Electric Highway" last week, and the new chargers allow for fast charging along Interstate 5. The chargers can take an all-electric Nissan Leaf from 20% charged to 80% charged in less than half an hour, enough time to grab a quick bite to eat on the road. When complete, the highway will run all along the West Coast, allowing EV drivers to charge up about every 25 miles.

That will help ease the worry for EV owners, but it still isn't as easy as filling up at the pump. That's what natural-gas vehicles can do, just the same as filling up with gasoline.

The advantage here goes to natural-gas vehicles, which will be quicker and easier to fill even if charging gets faster. And charging a large truck or a semi on even high-powered chargers? Forget about it.

Investing in the future of fuel
So what does all of this mean for investors?

Investors can take a leap of faith and buy a charger maker like AeroVironment or a carmaker like Tesla Motors in a bet on the electric vehicle. But I think the natural -gas vehicle highway will win this battle, and Westport Innovations and Clean Energy Fuels provide a great opportunity for the future.

For another great energy stock, check out our free report called "The Only Energy Stock You'll Ever Need." This company will profit, especially if a natural gas highway becomes a reality.