I agree with everything in EnergyNumbers' answer, but would like to add some more:
Along the lines of "easier to maintain", an electric motor is likely to last much longer, for example, in an automotive application, than an internal combustion engine (ICE). An EV traction motor may very well last 1,000,000 miles, versus perhaps one quarter of that for most ICEs. While it's true that current EVs tend to use batteries to power the motors, and batteries may need to be replaced at a comparable interval to an ICE timing belt, an EV with a new battery is going to run much more like a new vehicle than an ICE with a new timing belt. The regenerative braking associated with the electric motor will also prolong brake life.
Electric motors are more quiet than ICEs. This is a controversial topic. I believe noise pollution to be a problem, and thus, a quieter car to be better (especially with respect to sustainability). Some are concerned about pedestrian safety with quieter electric motors. While this can be, and is being, addressed by adding noise makers to electric cars, I believe this solution is actually misguided. The basis for this aversion to quiet cars partly draws from a multi-year study in the US concerning pedestrian accidents with hybrid vehicles. The hybrid vehicles had a 40% higher rate of pedestrian accidents than non-hybrids. However, the study did not correct for the fact that in the US, hybrids tend to be owned by city-dwellers, and the rate of pedestrian accidents is twice as high in cities vs. rural areas, for all cars. I believe this factor alone can explain the 40% result. Also, during this study, which involved thousands of hybrid cars, not a single blind person was killed by a quiet hybrid.
Size matters. In an application-agnostic answer, it's important to note that for some applications, electric motors are more versatile because of the variety of sizes they come in. Hopefully, it's obvious that an ICE to make your phone vibrate is not an option, but a motor works quite well.
Without specifying your application, I'll try to discuss multiple transportation applications. For cars or trains, the excess weight of a battery pack that drives an electric motor is not a huge penalty. The road provides extra normal force to balance the vehicle weight. However, in aerospace applications, power-to-weight ratio is more critical. So, for airplanes, using electric motors for propulsion is still not practical. Liquid fuels have a higher energy density compared to batteries, which makes petro-fuels or biofuels more attractive for airborne propulsion.
This is less of a problem for cars, which do not yet have to levitate. Also, it should be noted that comparisons of energy density for liquid fuels vs. batteries distort the true picture, because total weight is what's important, and an ICE system requires a heavy ICE, and a heavy transmission. When the whole system is considered, battery EVs suffer a noticeable, but acceptable, weight penalty for their lower energy-density fuel.
Battery range (capacity) is also a problem for EVs. However, I believe this issue to be exaggerated, as the average US driver (who drives a lot!) still only drives 40 miles on an average day. In the future, more charging stations will also minimize the range problem for electric cars. However, for now, range versatility has to be considered an advantage of ICE vehicles. An interesting compromise is made by Chevy's Volt EV, which is fundamentally an electric car, but which carries an on-board generator for recharging the battery by burning liquid petro-fuel.
Temperature constraints can be a disadvantage for electric motors, due to the batteries themselves. High temperatures can shorten battery life, and very low temperatures can (temporarily) reduce the useful capacity of the battery. Note that normal temperatures here on earth are well-suited to battery EVs, so this issue is more a problem if your area has temperature extremes.
This is difficult to answer without a more specific question. Electric motors will draw their fuel from different sources than internal combustion engines. Each country will have different economics regarding their electric grid, and oil consumption. If your country has more abundant resources to produce electricity (coal, natural gas, solar, wind, geothermal, nuclear), you may consider electric motors an economic benefit. If you're in an oil country, maybe not.
When you add biofuels to the mix, you add agriculture as a factor. Most internal combustion engines can use varying levels of biofuels. An Otto cycle engine needs modest engine modifications to run rich ethanol blends. Many modern diesel engines need no modifications to run biodiesel (although winter cold can limit the blend).
So, ICEs can provide a domestic economic boost if your country can grow its own biofuel feedstock.
I believe that pollution (which includes greenhouse gas) and energy efficiency are the most important factors here, and those favor electric motors for many applications. EnergyNumbers' answer covers those well. I simply wanted to add a few more pros and cons to round out the topic.
Disclaimer: biased owner of an electric vehicle, but I've certainly owned ICEs, too :)
A related question about Electric Cars on Sustainable Living
Note: more sources coming later ...
It is always cheaper to charge your electric car than spend money on gas for a regular car.
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You can find real-time comparison of average gas prices and electric car charging prices on the e-Gallon website.
Electric vehicles have other advantages over those powered by combustion engines:
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