The knots listed on this website are not always the best for a given use, as far as strength or security go. However, there are other important attributes that apply to some of them. These include:
Are they easy to recognise when tied?
Easy recognition means that you can look at a knot and tell that it is tied correctly, and even more importantly, when it is not tied correctly. Knots such as the double fishermans and figure-of-eight are easy to recognise as such.
Do other people know the knots?
If the knots are generally well known, anyone can look at the knot and check that it is correct. Most of the knots on this website are fairly well known to rope sport participants, so if there is a problem it will be easier to pick up. For example, some climbers tie into a rope with a double bowline - however, the rethreaded figure-of-eight is much more well known and is a better knot to use for this reason.
Are they simple to tie?
If a knot is easy to tie, you should still be able to tie it under difficult conditions. For example, darkness, or cold, wet circumstances. Most of the knots listed are relatively simple. With a bit of practice you should be able to tie them just about anywhere.