Have not been in the S chain or Agnes, but am familiar with PP, Burke, and North Bay.  Easy portages, fair amount of traffic, but the northern end of Burke Lake, where it narrows down, is my favorite spot.  I think that is just because in my mind it is the entrance to the wilderness.  At that point, I have left behind the motorboats, phones, and rest of civilization, and am embarking on a journey into the wilderness.  If you are looking to camp in Burke or North Bay, the pcd has good data.  There are several nice sites.  Somewhat heavily used, but pretty good shape considering the use.