Radio controlled helicopters, or RC helicopters, are a staple for radio-controlled enthusiasts. If you're just getting started in this most enjoyable hobby, there are few things you need to know when you're looking for your next (or your first) RC helicopter.
Gas, or electric?
RC helicopters are available in either electric or gas powered models. If you're just getting started in the hobby, the electric powered models are easiest to handle. They're quiet and fast, and you don't have to worry about gassing your helicopter up or having to fine-tune the engine on a regular basis. If you wish, you can get into those finer details later, once you get more experience.
Flying RC helicopters
The best part of having RC helicopters is learning how to fly them. As you go, you'll learn how to do this well, but you may have a crash or two while you're still learning. Don't spend a lot of money on your first purchase and instead focus on using that one for practice; as you get better at it, you can buy kits when you decide to build a new one. This will give you the opportunity to tweak and play with options for helicopters, once you know how they work.
Finding RC helicopters for sale
The best place to look for helicopters for sale (especially used models) is on the Internet. Lurk on forums specific to the hobby, and ask around. Those forums may have information that can tell you whether or not there's a local club for RC helicopter enthusiasts nearby, in your area. If so, this is a great chance to commune with likeminded individuals who can actually teach you something about your new hobby, too. Even if you can't find a club, you've probably got someone local to you who can help you buy an RC helicopter from sources they use (or through them, if they're selling) and collaborate with them, to have them teach you how to experiment with RC helicopters and have fun.
Collective or fixed pitch?
When you look for RC helicopters for sale, you have an option to buy those with either collective or fixed pitch setups. The pitch is the main rotor blade's angle; helicopters get their lift when blades rotate through the air.
With a collective pitch, the rotor can change its speed at your direction, and it will give you a more agile, responsive, smoother flight. However, it's more difficult to learn how to operate a collective pitch, and it's got moving parts and a much more complicated transmitter than the fixed pitch gives you.
With a fixed pitch, the rotor pitch is fixed and not changeable; more lift is generated with a faster spin, and less lift is generated with a slower spin.
If you're just getting started with your radio controlled helicopter hobby, start with a fixed pitch, because it's easier to learn how to handle. Once you gain some experience, you can opt for a collective pitch instead.