As the PM managing your property has knowledge of the tennants and possibly knows / trusts the tennants and vice versa I would have though generally it is better to go with them at least if they think they can manage the tennants that is.
A third party arranging visits inspections will find that process harder I would have thought without all the forms of contact a managing agent has usually put in place with a tennant, emails, phone, mobiles, spouses phone etc to arrange last minute inspections etc.