There was a recent thread about obsolete file formats. In that case the topic included pictures and word processed documents. In computing, there is always the possibility that a new format (or new programmes) will become popular, and the files you have saved with an earlier format will not be supported by the new set-up. Microsoft are notorious at trying to cripple anything which is not from their latest most expensive version of Word because they want to force everybody to buy the new one. They seem to have made Vista incompatible with favourite programmes used by numerous mudcatters.
Looked at in this light, any format you choose could, in the long term, turn out to be the wrong one. You may need to stay up to date on the technology and periodically re-convert to the "new" file types.
Quack!
GtD.