A lot depends on what equipment you have to read the data with. I double wipe all my customer drives, random patterns, every bit, every sector, every track, every cylinder.
No exceptions.
If the drive is broke, I really break it ... into pieces, then make sure to bend the platters completely.
I used to design and manufacture hard disk drives. You might be surprised what can be recovered. I take the side of the software manufacturers, I think they are doing it safe.
You have some knowledge of Professor Peter Gutmann’s work on secure data deletion and recovery, has Gutmann been promoting snake oil for the last decade?
http://www.cs.auckland.ac.nz/~pgut001/