I've tried plenty DVD+R DL discs the last few months, and like Dee said, ONLY the Verbatims worked fine. They burned okay and were readable in all players (with DVD-ROM bitset).
Don't buy cheap DL discs (RITEK made).. they burn horribly and are not very well readable in most drives.
I learned this the hard way, after wasting 5 of the total 8 Ritek discs, and the Verbatims work great.
Since Verbatims still are pretty expensive, the cheapest is maybe 7-8 euro a piece you'll be better off buying the original often.
The choice between 12 euro for an original or 8 for a burned disc is not very hard. Of cource, when the DL discs get better and/or Verbatims get cheaper this will change..