which is the correct blank disk?

esuhl

There's not much difference in functionality between DVD-R and DVD+R (so long as your machine supports both types).

DVD-R are slightly more likely to be compatible with standalone DVD video players.
DVD+R use slightly better error-correction algorithms making them slightly better for data storage.

In day-to-day use I've never had a problem with either format.

I have had problems with CD-RW, DVD-RW, DVD+RW and DVD-RAM. I just don't think rewritable disks like me... or maybe they just don't work. I've given up using them now and stick to the write-once variety.