javascript mongoose Most Efficient between findindex and updateOne

I am updating an array inside a field but I am looking for which one is the most method efficient with respect to system resource and speed between.

method 1. 
UserModel.updateOne({
        _id:studentSelect
    }, 
    {$set:{'contact.$[first].state':'California',
          'employment_detail.$[second].employment_date':Date.now}},
    {arrayFilters:[{'first.dept_id': thisidthedeptid},      <---array filter to get specific data
                   {'second.dept_id': thisidthedeptid},]}

.

method 2.
var contactIdx = usermodel.contact.findIndex(x=>
            x.dept_id==thisidthedeptid)
var employmentIdx = usermodel.employment_detail.findIndex(x=>
            x.dept_id==thisidthedeptid)
usermodel.contact[contactIdx].state = 'California'
usermodel.employment_detail[employmentIdx].employment_date = Date.now()

Please this is not for a debate or some thing like that. I want to know which one I should stick to. And please state reasons for it. I could not run a test on my system