algorithm is the best (as in most destructive to data) way to erase data.
I use DoD 5220.22-M
algorithm to erase data. It isn't the best, but most of the data won't be recoverable.
If the drive is not important to me, I usually try to dismantle it (deforming the platters in the process), and putting a magnet directly on the platters.
The absolute best way to destroy data on a hard drive and likely the hard drive too is to use a degausser. They often cost $3000+ though so not very practical for small outfits. If you want the best of the best, find a degausser that has the NSA (National Security Agency) seal of approval. Here's an example of NSA approved
device and it runs for over $21,000: http://www.datadev.com/degausser-sdd-master.html