What is the best Beginner RC Helicopter?
If this is not the most loaded RC helicopter question of all time, then I don't know what is.
This is one of the most popular posts to make for beginners on user forums.
What we are talking about here is an RC helicopter for someone who will become a Hobbyist Lets say this is you. Not your 8 year old nephew that your looking to buy a birthday present on. This advise will not help you much with that decision, which should be a gift card anyway cause that's what they want :)
15-20 years ago, the answer was simple. The local Hobby shop only had one helicopter or you maybe ordered something from a large phone order catalog. Times are good for RC and now the choices are large as well as changing every year.
There is no one answer that fits everyone.  There are a number of factors that should go into the recommendation and should not be ignored.  Simply answering "What is the best Beginner RC Helicopter" and then answering it with "Helicopter X" is in my opinion a bit shall I say unfair? Or maybe just ignorant? Ok, maybe I will use the word "Inexperianced" of the advisor who is not learning more about the person before making a recommendation.  Many times, people will recommend what worked for them and use words like "Get this and you will not be sorry".. Their situation can be vastly different than the person asking the question.

Factors that should go into the buying decision are:
  1. How much $$ is in your budget for your first helicopter?
  2. How much $$ is in your budget for future helicopters? (if you think you might stick with the hobby, will you continue to persue the hobby and then spend $$ a year on this hobby?)
  3. How old are you? (Although I've seen people who are 50+ learn RC helicopters, Generally, the younger you are the faster you can learn as well as the better your vision and hand/eye coordination)
  4. How good is your hand/eye coordination?
  5. How good is your vision?
  6. Do you have a large indoor area to fly in? (Barn, Warehouse,  2/3 car garage?)
  7. Do you have a wind sheltered outdoor area to fly in? (Large covered carport, Side of a building, Backyard surrounded by tall trees etc).
  8. Do you have local resources that might be able to help you out? (Friend, Flying Club, Local Hobby shop [that knows what they are doing])
  9. Do you want to get local parts for your helicopter or Internet/Phone order only?
  10. Your buying mentality? Do you like to buy one thing and be done with it, or do you like to progress your way up, giving you time to change in the future?
  11. Previous RC Airplane experiance?
  12. Something else ??????
Some of the above factors are more important than other like Budget and available flying area are the bigger things that influence a recommendation I may make.

Lets start off with 3 types to choose from.
4 Channel Coaxial(Coax) -> 4 channel Fixed Pitch(FP) -> 6 Channel Collective Pitch(CP)

Notice how I show that progression from 4 Channel Coaxial to 6 Channel Collective Pitch.  On the left is the generally least expensive type to buy, and on the right is the most expensive type to buy. Not only is there that progression, but it also is ordered in the easiest to the hardest to fly (in general) as well as fix.
Some will say that there are FP helicoptes that are HARDER to fly than some other 6 Channel CP helicopters. I can not deny that statement.  In recent years (and even months). The division between Coax and FP stability has become smaller. FP helis like the Walkera CB180 and Xheli's Madhawk 300 line have shown stability charactoristics rivaling Coaxials.  
As mentioned in the list of Factors. Where you fly has an influence because Helicopters are subject to affects in the wind.  Here is a breakdown of how they might be used:

* Collecitive Pitch helicopters can handle more wind when you can handle the wind.  Larger CP helis can handle more wind but it is not advisable to train in the wind until you are ready for it.

Here is some general information on each type of helicopter and some of their charactoristics:
Coaxial The most inherently stable type helicopter. 2 counter rotating blades generally are driven by 2 seperate brushed motors. These helicopters can not move laterally (side to side) very fast so are very susseptable to wind dragging them off. When learning on a coaxial you are mostly learning the left stick which changes rotor RPM to climb/drop as well as yaw (rotate) the helicopter.  Some people swear by starting with an indoor coaxial (if you have the room) while others will say they were quickly boared with it. If you have the room for it, starting with a coaxial will nearly never be "too much" of a helicopter for any teen or adult. If so, then you would want to rethink finding another hobby.  Having an indoor coaxial in the winter months for the northern climates can come in handy to get your "heli fix" in the winter months if a simulator does not do it for you. These helicopters might come as "bind and fly" (Require you to have a compatible radio) or RTF (Ready to fly including battery and Radio). Generally, many mishaps/crashes will result in zero damage if you drop the throttle at or just before the moment of impact. Coaxials at Xheli E-flite Coaxials
Fixed Pitch A fixed Pitch heli has a fixed pitch set of rotor blades and a Brushed or Brushless motor to drive it. It will have a motorized tail blade typically that is driven by a 2nd motor.  Fixed pitch helis are typically a stepping stone to CP helis. Many people later come back to enjoy their FP heli to become a park or backyard flyer when there is little or no wind. Fixed pitch Helis hover more like a conventional CP heli and allow slightly faster forward flight. They are cheaper to repair because typically, less things break in a crash.  Generally, many mishaps/crashes will result in zero damage if you drop the throttle at or just before the moment of impact.  2 types of FP are emerging. Flybar with paddle (Esky Honey Bee FP, Falcon 40). Flybar with weights and no paddle (Walkera CB180, Exceed Madhawk 300) The CB100/MH 300 although more stable than a HB FP, they have less forward/lateral speed so they should be flown outdoors on only the calmest times (<3mph) unless you modify the linkages to allow for more forward/lateral speed.
Collective Pitch The Collective Pitch Helicopter has a motor which drives the rotor RPM but the pitch of the blades vary with stick movement. The left hand veritical stick controls both in tandum and is mixed electronically in the radio. Ultimately, this is where you will end up if you continue to persue the hobby. CP helis come in various sizes from tiny Micro palm sized helicopters to larger .90 nitro helicopters. The most popular size to learn on if you decide to go CP is the 450 size.  Originally named for the size of motors used, these helicopters use 315-335mm blades (325mm is typical).   In general, bigger is more stable, faster, more expensive to buy and fix as well as more dangerous for the novice pilot.  If you think you might want to start out on a helicopter larger than a 450 sized helicopter, you most definitly seek out multiple sources of personal advice stating why you want to and listen to opinions before doing so.  Lots of people have skipped over the Coax or FP heli to learn on a CP.  There are also those that started on a CP, were frustrated, then stepped back to a FP or Coax. Generally, many crashes on a CP heli result in multiple items being replaced which requires both more time and more $$ to repair as well as knowlege. Example of a 450 crash part list. Many of the 450 sized helis that people are learning on can be upgraded to better motors,servos, gyros, blades ETC as the hobbyist progresses to where those upgrades will realize more benifits. Examples of popular 450's : EXI 450 , Exceed Blueray, Align Trex 450, E-Flite Blade 400

So are you headed to conclusion or confusion yet?
At this point you should be at least down to one of two categories if not already rifling through product pages looking at different helicopters. Maybe you've been spending an hour (or more) searching on youtube to look at videos of helicopters and how well they fly in the hands of a Novice? yes, Novice. You will see many videos of helis flown by the experts but how well will they fly for the novice?
Here is an instructional page on what a beginner Heli pilot will go through in their Training (example is with a CP 450 heli)