When to use “staffers” vs “staff”?

"Staff" and "staffer" are essentially the same, but they are slightly distinct.

"Staff" is defined as:

All the people employed by a particular organization. [Lexico]

Therefore, "staff" is a collective noun (such as "family" or "crew").

"Staffer" is defined as:

A member of the staff of an organization, especially of a newspaper. [Lexico]

Therefore, "staffer" refers to an individual member of a staff.

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Once you account for the fact that "staff" is collective (as you did in your sentence), the sentences' meanings are identical. Personally, I would use "staff" because it is much more common [Ngram].

A staff is a group of persons under command and control of a single person or an aggregate of persons who operate as a unit. A staffer is one member of a staff. Complexity comes into this picture in two ways. If the term "staffers" meant to be inclusive of all members of a staff with no qualifications this would make the use of the two terms interchangeable since they each refer to the entire staff. A reference to some qualification of staffers, such as "full time staffers," etc. would be a different intention. Note that the term "staffers" might also be used to describe a specific job of evaluating, hiring, or denying persons applying for employment or advancement in a company. This use of the term would make all "staffers" taken as a group a staff of, say, the manager of a Human Resource department or division. It is unlikely (perhaps humorously) that such a manager would think of "staffers" as his "staff" and would likely only use the simpler term "staff" to refer to them. For him the two terms would mean the same group of employees. For the head of the company, however, the two terms would mean different groups of employees.