We know Adobe is trying to improve workflow by including the Main Concept MPEG2 encoder in AE 6.5 for Windows. In theory it sounds like a great idea to go directly to MPEG 2 but don't rush. In order to get the highest quality and smallest size , you need to perform a two pass Variable Bit Rate encoding (VBR). This approach works by analyzing a file and then compressing it. So unless your copy of After Effects is clairvoyant, you can't analyze a file before it's rendered. Always go to the Animation codec, and THEN convert to MPEG 2. Remember, slow and steady wins the race (at least it always worked for the turtle on TV).