An additional benefit to flying online is social interaction. A large factor in your decision may be cost. Retail packages usually offer free online play, while the dedicated multiplayer simulations, after a grace period, will require you to pay a periodic rate. The chart on page 20 lists subscription plans for popular simulations. Performance and quality.
Online games can suffer from something called lag or latency.
This phenomenon, known as warping, ruins the fun, fairness and realism of the game. Warbirds, the most expensive simulation, is one of the smoothest performers. Aces High, built by former Warbirds developers, is also a stellar performer. You'll witness warping in any online game, but in these two it is rare and less pronounced. Mplayer, in contrast, offers free hosting of MiG Alley and Flight Simulator 2000, but its connection stability and performance are poor.