I've been using Valve Network's Steam service for over ten years now. And without fail, Valve has delivered every single time I've purchased a game. While they've had their share of security concerns, they still somehow manage to deliver an exceptional game purchasing experience again and again.
To put their reliability into perspective, I've had more power outages that Steam outages in the last ten years. THAT says something. Kudos to Valve for a job well done.