It depends on what type of customization you need.
Before methods are the first methods to run in an observer method. You can return a modified argument. If there are multiple arguments, the returning will be carried out according to a range of those arguments. If the returning is invalid, that means the arguments for the observed method should not be modified.
After methods start running right after the observed method is finished. After methods take a responsibility of editing the results of an observed method in the correct way and being required to have a return value.
Around methods allows the code to run before and after the observed method, so you can override a method. Before the arrange of the original method’s argument, a callable from around methods will be called to the next method in the chain, that means the next plugin or the observed function is also called.
In Short
If you want to modify arguments before running function then you
should use before method.
If you want to change output of function, then you should use after
method.
If you want to change both arguments and output of function then you should use
around method