I suppose that's a personal choice. If you don't get a work study job you can always go back to financial aid and get them to review your file and increase your loans instead. I always liked a work study job, because they are easier to find around my school than regular jobs with the flexibility and semi-decent wages, and since I live on campus I didn't have to deal with taking the bus or getting a car just to go to a job. And work study also meant not having to take out as many loans which makes the possibility of loans last longer (I'm a nontrad so I'm starting to get close to the max for ugrad).
Workstudy income counts just like regular income. If you make 3K in regular income one year it goes against the following years total aid package. If you make 3K in workstudy income one year it goes against the following years total aid package. But neither of these really affects the total amount of loans you are eligible for since you can typically borrow the amount of your EFC regardless.