I will be getting an Apple TV. I buy Blu-ray discs for all of the movied that I know I want. There are, however, quite a few movies that I would like to see, but don't want to spend $24 to $35 for a disc. I will rent those movies. Renting online is the most convenient way of achieving this.
Check out this web site. This guy thoroughly compared the differing formats for several movies, against Apple TV.