Take a look at my sig, last link, leads to a transcription of the last C't study, longevity (climatic) tests included.
Looks like 8X -R Verbatim MCC 02RG20 is the king of longevity among good discs. Apart from Princo, the most bashed media recently here is Ritek G05. But these two sentences of mine are only a poor summary of this complex and very debatable subject.
There are several threads in this section discussing this topic actually, you could search around for "longevity", "degradation", "data loss", "lifespan", "reliable" etc...
Also read the media FAQ. :iagree: