Hi
As Dirk said before, if you're running unstable, the official version is surely the best.
If you're running testing though, you're probably better off using the apt sources listed in http://cran.us.r-project.org/bin/linux/debian/ReadMe since there are some dependency hassles with installing the unstable version on testing (at least I got tired of going through all the dependency stuff).
Cheers,
David