Both Count() and CountA() functions counts non-blank values but works with different data types.
Count() = works with Numbers, Dates and String data types only
CountA() = works with All data types
CountRows() counts all the values including blanks.
CountX() allows you to write expressions in the function
Each function has its own use case so depending on whether you want to count non-blank rows only or all the rows or what’s the data type of the column against which you are going to count and whether you have an expression to be evaluated helps you decide which function is a good fit for your scenario.
If there are NO rows to count, each of these functions returns BLANK value, otherwise, they return either the count or zero depending on rows satisfying the condition.