There are a number of fork types each designed for its purpose, and they are as follows;
The Garden fork:
Similarly they are generally not quite as pointed as the muck fork.
As with the spade size and weight is important, but as a tool, it is not as essential as the spade, unless your soil is heavy clay.
However it must be said that a fork may fail at jobs such as breaking up exceptionally obstinate clay clods.
When faced with such a situation break the clods with a pick / mattock or leave them to weather.
This type of fork has four round very sharp tines, and is generally used, as the name suggests, to collect, spread or move farmyard manure or organic matter.
When harvesting potatoes and root crops either of these two types will suffice, although you might find you get better results with the flatter /wider tines of the garden fork.
Subsequently it is generally only used by commercial potato growers, or people who have to handle large amounts of potatoes.
It normally has 8-9 ball bearing tipped tines to prevent the tines spiking the potato tubers, plus the tines are bent to form a shovel effect.
This is a diminutive version of the garden fork and quite often has round tines like the muck fork.
This makes it a handy tool for forking in manures and fertilisers during the growing season, its size makes for easier work between rows of plants.
Which one to buy?
Possibly the garden fork as it can handle most of the jobs that the other specialist forks were designed for!
As with the spade the handle and tines should be thoroughly cleaned before the tool is put away after use.