ATC Watcher, avoid the roads between 0600-1000 and 1600-2000. If the Stansted Express is running (it doesn't run very late/early and isn't too reliable), I hear it's an OK service, the Gatwick Express (expensive) or a normal Gatwick train (from Victoria station) tend to be more reliable. But, if you're not travelling light, lugging suitcases around the underground isn't much fun! And you'd better have a plan B (maybe that heli) in case the Stansted rail link is stuffed.
Good luck
