well, IMHO, putting everying in a single 300GB HDD is risky. I would rather consider backing up to both HDD and DVD.
HDD often crashes without warning, or sometimes the whole file system might corrupt due to unknown reasons. Backing up to two location or two types of media should be safer. At least i know that the DVD is there when HDD crashes
If suay suay both also fail.. then really bad luck liao.
As for brands of HDD, i used to buy Quantum, then Maxtor. But now i move on to Western Digital. Had a 30GB Maxtor that failed and a 40GB Maxtor dying.