Give me high capacity single write discs that are good for a minimum of ten years. I've got Kodak Gold CD-R's that were guaranteed to last for ten years, and the backed up data is still OK now, a few years past their guarantee. Single write because I've never been a fan of RW optical media - all too often it's just never quite worked right for me.
Problem is, initially discs'll cost a fortune, even if the drives themselves are cheap. For the sort of prices I'm sure they'll command, they'll need to have double or triple that capacity. Not to mention... 2015 is a long way away, and data has a chance to get much bigger before then.
Flash media backups are still not trusted for long-term storage. I've had a couple of USB sticks refuse to work recently. Didn't use them for about six months, go to use them again... and they simply don't work. Reliable models, too. I had everything that was on them elsewhere, because a backup isn't a backup if there's only one.
Everyone will have their own preferences; I use flash memory storage all the time for quick transfers, but fall back to single-write BD-ROMs or NAS for longer term backups. While 50 and 100GB BD-ROMs are still horribly priced (£38 for one 100GB disc?! You're having a laugh, Panasonic!) the 25GB discs are pretty reasonable now.