What are you looking for? Peace and quiet (with nice beaches) or loads of shopping and manufactured things for the kids to do. If it's the former, go to Truro or Wellfleet (and get there by taking the fast ferry from Boston). If it's the latter, Chatham (which has access to all the craziness and tickytackiness of Hyannis and Harwich). Personally, Wellfleet is my favorite town on the Cape. Beautiful beaches, just enough of a village to keep things interesting (which Truro is sadly lacking), but not too far from P-town or Chatham if you want tourist craziness and more meal variety. Plus Wellfleet has the drive in
Newport is gorgeous, but IMHO the beaches aren't as nice. If you look at Newport, I would try to get somewhere near Gooseberry Beach. Easy enough to get to downtown, but fairly quiet part of town.