The current industry “default” is Quicktime .mov with the Sorenson 3 Codec. This is what you’ll find most often times used in the Apple movie trailer section. People will argue this with me, but that is what we use at our company. (Doesn’t hurt were a Mac shop either)
Blender can render to this format and codec on any windows or Macintosh machine.
Although buying Apple QuickTime Pro (USD 30) is great because it becomes the swiss army knife of video converters. Rule of thumb: if QT Pro can’t convert, you shouldn’t be using it!
Divx offers good compression, but users will have to download the codec and Divx and Macs do not always play nice with each other. So if your going to be sending it to anyone that possibly uses Macintosh, I recommend avoiding.
Likewise, Windows Media Player usually will play on a Macintosh, but MS as dropped support on the Mac platform. A third party is now providing a Quicktime plugin for Mac that actually performs better than MS media player for Mac did. So, yes, this is a possible choice, but I still like the quicktime wrapper and Sorenson 3 Codec options better.