I do a bit of both, running and completing. If it's a public area and everyone else is running then I run too. Other than that I tend to kill most things but it often depends on the other two players actions. I'd rather work in a team where I can so if that means one guy races ahead I'll chill and kill things with the 3rd person. That 3rd person might be doing a kill x amount of bad guys or just having fun.