Only real experts should do it the soft way.
If the drive is old enough there is no value to the storage space and remaining life span it offers. In that case the hard way of destroying it is definitely the method of choice - my favourite implement of destruction is the angle grinder - a rotating disk destroying a rotating disk ...
But maybe you do want to reuse the drive or give it to someone that would - but then you should donate the whole computer. In that case the soft way is the way to go. But it requires a good deal of insight into how data is stored on disks and how to get rid of it. The biggest gotcha here is that most ways of deleting data or even whole partitions just release the space containing the data for reuse by overwriting the directory or partition table information. Don't fret if you haven't heard these words before. All I am saying is that the data is still there but can't be found by the conventional means. But to experts - or users of programs written by experts - it is no challenge to get it all back - or at least most of it. So the trick is to also overwrite the actual data. This is not too hard but will be time consuming.
Yes you can buy programs that erase the data on the drive several times over, in line with DoD standards created decades ago when drives still worked differently. On reasonably modern drives and for data that isn't worth millions to an intruder a single complete overwrite should be sufficient. So, someone sufficiently computer-literate might do some or all of this:
- Run your computer from a different drive (or attach your drive to another computer as an additional drive.)
- delete all partitions on your drive (make sure this and all teh following happens to the correct drive - or else!)
- Create one partition covering the complete drive.
- format that partition with the "biggest" file system available (use NTFS if possible rather than FAT32, for instance.) For good measure, don't do a "quick format."
- Fill all available disk space with uninteresting data - use some big file you have and make enough copies to fill all space. Add smaller files to fill up the slack. Now all your data has been overwritten.
- Then, to confuse any attackers, delete all the files again, delete the partition and create several partitions on the drive (two or at most three should be optimal, depending on the size oif the drive.) and format them, possibly now using a different file system. Put a few unintersting files and directories on the drive, some of which you delete again.
Now if any attacker would use disk analysis software to find out the secrets of your drive he would find some hints of the files you put on last. Maybe he would also find traces of the big files you put on to erase all deleted data. But there is nothing left of your original data to suggest it was even there. Even the old school drive analysts wouldn't find much by "reading on the grass" (grass = the area between the written tracks that according to some may still contain traces of overwritten data since the heads are never aligned quite so precisely - hence the old rule hat you must overwrite your data seven times with different bit patterns - probably total overkill in your situation.)
I told you the angle grinder is quicker - and much more fun ...
If your community runs an annual fair, possibly you could also rent a stand there, get yourself lots of old hard drives from whatever sources (working or not) and offer the use of angle grinders and hammers (BIG ones!) for a fee. People can then come and buy a ticket to destroy a hard drive to reduce their own stress or agression levels. They can bring their own drives as well - if you are in the US, get them to sign an indemnity form, in case anything untoward happens - like they brought the wrong drive or the one belonging to their Ex ...
Then donate the money to charity and feel good!