There is no should or must be this way or that way correct answer to this question. It's up to the designer of the database and software.
As for me, I usually use singular names becouse when I do the E-R diagram I have an entity Customer , not Customers, so I keep it same as to not get confused.
Ofcourse some frameworks do favor one style or another, so you should be best of to follow those practices when you notice them.
