in tenafly, the outdoor basketball courts on tenafly road near riveredge road are always busy. lots of people come from neighboring towns (englewood, teaneck, bergenfield) to take part in pickup games at these courts.
there are also two outdoor courts in closter. one of them is on harrington avenue just west of the downtown area/railroad tracks; the other is on ruckman road on the east side of town. as i recall, the harrington avenue location tended to be busier, but you should check out both if you're in the area.
for indoor facilities, you may want to consider hoop heaven on hopper avenue in waldwick, which is a popular spot for adult and youth basketball leagues and youth summer camps (never been there myself). while i'd assume that there are plenty of pickup games since the place is focused on hoops only, you should contact them to find out for sure; it might be open only to organized leagues, camps, and clinics.
i don't know how much it costs to become a member, but here's the contact information:
hoopheaven.com
also, the 24 hour fitness gym on route 17 south in hasbrouck heights has a large indoor basketball court. i would suggest searching online for a guest pass (they usually offer 1 or 2 week trials) and then checking out these courts for yourself.
whichever place you end up choosing, please make sure to check back in here and post your findings for the benefit of others.