What is a good flight simulator for a beginner?
Most commercially available flight simulators (MS FSX, X-Plane, Prepar3d) can make excellent training tools for a budding pilot.  But do take this caution to heart.

The cup has to be empty before it can be filled.

Applied to flight training, do not attempt to instruct yourself how to fly.  At best, you will develop a lot of bad habits which a CFI will have to root out and correct prior to being able to teach you correct airmanship techniques.

On the other hand these kinds of games, when set to use realistic flight models, can be excellent tools for practicing skills you learned when you flew with a CFI in the real thing.  Using a realistic simulator game in parallel with real world flight training can save you a lot of time and money in your training.  These sim games are also excellent for instrument training as much of the required instrument skillset is easily modeled by the computer.  While not approved as an official Flight Training Device for logging official flight time, these sims are extremely realistic - so much so that the same mistakes I make in FSX I will make in the real thing!

One cautionary note:  sims like FSX do model a number of details correctly whereas other ones like dangerous weather, flying at the extreme edges of the envelope, etc are not.  There are a number of scenarios (eg flying into thunderstorms) you can do in FSX which will get you killed in the real world.  Approach learning to fly in a game with caution and any instruction you receive from a CFI should supplant game derived knowledge.