I'm an advance beginner flyer. I have FS One and Aerofly and used to own G2, but haven't seen the newest version of Real Flight.

If you a beginning to intermediate flyer, all 3 will teach you what you need to know, i.e. stick movement.

Aerofly has the largest network. Good support and tons of aircraft. Instructions are available on how to build your own planes and many have done the work for you and offer them for nothing. The software vendor support those efforts and link to many free add-on sites. http://www.aerofly.com/www/free_stuff.html

Most of the stock planes are Europeon, but users have done a ton add-ons. Innovative stuff like the Wright flyer, the whole Multiplex line and many, many US aircraft.

It also installs with 2 CD's, FSOne has 4. Aerofly loads in 1/10th of the time it takes FSOne to open.

FSOne is prettier, but not by a lot. Most say it has better aerodynamics, but again, a novice won't notice. In that regard, all 3 will probably perpetually leapfrog over each other.

One thing that perplexes me about FSOne is how anemic the help file is. It identifies each screen in the program, but there's almost nothing about how to use any of them. A detailed well written manual would be a nice addition.

For me, a sim doesn't have to model flight characteristics perfectly. I use it to learn stick movement and how to stay out of or get out of trouble.