I can assure you vatsim is the best. But if you dont know how to fly properly or you dont know the CORRECT ATC procedures (not the FS ones!) then dont try and use it without getting some lessons first. BAVirtual are good for that, website at http://www.bavirtual.co.uk
You cant compare any of the FS traffic addons, purely because you are talking through a microphone to another human being. There are many pilots, and there are many VATCO’s (the ATC guys!). It is serious, and although its a game, its a very serious game. Nothing better than flying online with real air traffic controllers and other real pilots flying for many different airlines.