Need to rent a car for about a week from one of the NYC airports - JFK, EWR or LGA. My choice of location to fly into.

Any quick suggestions which location will run cheapest in September? Maybe taxes in EWR are higher or lower than the NY state ones etc?

Any suggestions which rental company seems to offer best deals in that region? Car will be dropped off at point it is collected at.
Thanks in advance for the fast advice!