All these are great choices. There are so many airlines to pick from.
I wanna join so many but staying with one gets boring. I only limit my self 3 but I found this great one that had like 20 airlines with it all on one virtual airline.
http://simairline.net/There real with THE REAL AIRPLANES THE COMPANY USES and its greatly put together.
The second VA im with is the Air Canada above a few. Its a bit more advanced but you had to pass a test to join.
My third is jetBlue Virtual Airline which im near leaving pointage ;D
Hope this helped if you plan on joining PM me ill be great to hear and we could fly online together!
8-)