RC cars can be a very enjoyable hobby providing you make good decisions about the car you build. You will have to make a lot of decisions as you build your car, depending on how serious you are about your hobby. You can build an inexpensive car that you just drive around an empty parking lot or you can build an expensive car for racing. One of the biggest decision you will have to make is how to power your car. You have a bunch of choices for your engine with a huge range of cost and performance.
Most beginners start with cars that are powered by batteries. Battery powered RC cars are the slowest of any type of car but they are also the lightest. This means that they handle the best and are the easiest to drive. Batteries are also the cheapest option; this makes them an ideal choice for beginners who are just learning how to drive an RC car.
As people get more serious about RC cars and especially as they start to get into racing them they usually upgrade to gas powered cars. A gas powered RC car is much more powerful than a battery-powered car and therefore much faster. The downside of gas-powered cars is that the engine is heavier than an electric car making them less agile. Another downside of gas is that the cars are very loud, although this is an attraction for some people. Gas motors are fairly common, so it is easy to find a kit at your local hobby store.
For the serious RC car hobbyist, the next step up is to nitro engines. These cars are even more powerful than gas-powered cars; they are also heavier and even less agile. Serious RC car racing pretty much requires a nitro engine in order to reach maximum speed. The major downside of a nitro powered RC car is cost; they are fairly expensive. They also wear out quickly and will need to be frequently replaced.
In general, it is fairly easy to change engines in an RC car, so it is pretty simple to switch to a different type of engine. A lot of RC hobbyists have a wide variety of engines and change them frequently to suit their needs. Therefore your engine decision is not critical since it will probably change as your needs change. The most important thing is to choose the right engine for your intended use of the car. This will ensure that you get lots of enjoyment of out of your hobby.