My advice is avoid Dolby TrueHD. DTS-HD has a plain DTS core inside it, and allows it to play on older equipment, while TrueHD isn't much use to anyone without HDMI capable surround equipment, because you'll have to include a seperate Dolby Digital file. To be honest though, a full bitrate DTS file is more than adequate in almost all situations. And with the number of different audio options you usually provide, full bitrate lossy DTS will provide enough space for all of those options. I would suggest that you provide YOUR preferred option in a 640kbps Dolby Digital option, so that people with even older, non DTS capable equipment also get the best out of their system.

For anybody who has not yet made the jump to an HDTV yet - Get yourself a bluray player anyway. It is amazing the image quality difference, even watching Bluray content in standard definition. The extra color information alone provides a much more vivid viewing experience. And Harmy's edits deserve to be shown in the best setup you can possibly show it in :)