Prussic knot if often overlooked in favour of Klemheist. It can be prone to jamming in certain circumstances, for instance on wet ropes, and thus be difficult to move when speed is a factor. However, it has its place in some situations, particularly as it is possible to tie with one hand.
French prussic is the most used prussic knot. It is quick to tie and doesn't jam. Most climbers use them while abseiling as it can be easily controlled with one hand. It is tied by making 4-6 loops around the rope with both ends attached to the carabiner.
Knot under the load biting the rope:
Klemheist is a very useful knot sharing lot of similarity with the French Prussic, although with one major difference. It is not possible to be released when under the load. The knot is best tied from the top downwards. A small loop is held against the climbing rope and rest is wrapped neatly downwards. The long line is then pushed through small loop and clipped on to a karabiner.