Cheshire, I would NEVER leave my car at the Newark airport public parking lots. I always park off site. I've used several places, right now I'm using SkyPark as they have a deal where you park ten times and get the 11th free. I used to use Vista and loved them, but had an incident where I called for over half an hour once before they would answer the phone (let it right 11, 12 times), at midnight, so I don't use them anymore.
There are plenty of other places as well. The airport lot isn't secured, there was an article in the Star Loser a couple years ago about how massive the theft and breakin problem was there.
Anne