I've heard nothing but good things about Northern Westchester. My sisters and 3 cousins delivered their babies there (a total of 8 births) I was present for 3 of the births.
NWHC is also a Designated Planetree Hospital (dedicated to patient-centered and family-focused healthcare). One of my cousins actually had complications (e-clampsia) and her treatment there was outstanding. The baby was actually released before she was and the hospital actually allowed her to keep the baby in the room with her if she chose to (they provided a bassinet stocked with diapers and food in case the baby stayed).
As far as Putnam, I dont have any experience with them. For regular hospital stuff (ER and surgeries) I've heard from co-workers about bad experiences but I dont have any first hand knowledge. I should add though, one of my cousins who delivered in NWHC lives in Brewster but chose NWHC instead even though PHC is obviously much closer...
I also have heard nothing but great things about N. Westchester. I know 4 women who have delivered there and all had great experiences. it really depends on what type of labor and delivery you have in mind. Some women want to experience a natural, drug free labor and some know off the bat they want to have access to an anesthesiologist and meds. Depending on your OB and your idea of what you are looking for will help make that decision. Some hopspitals to not specialize is natural births or vice versa. Chek em both out you have plenty of time...take care and good luck