The Marriott at Newark you can walk to the terminals (its maybe 5 mins) The renaissance has a shuttle, lots of airline personnel stay there. It only 10 mins to get there, but the shuttle runs about every 20-30 minutes so timing is critical. The other Marriott properties (Faifield, Springhill, etc) are further way and the ride is more like 15 - 20 mins and they also run about 1X every 30 mins. You can call any of the hotels and see how the shuttle works, and they will share the info inf you tell them flight (airline) and time. Then you can plan accordingly. I have stayed in every hotel Marriott has at EWR and the Marriott is the easiest since the terminal is a walk thru the parking lot. I hope that helps
I've also stayed at the EWR and agree that if price/points are not an issue, this makes the most sense. Courtyard and RI in Elizabeth are both short shuttle rides (across from each other) and these are the hotels that most flight attendants and pilots use. These are very inexpensive $ or points, and have the advantage of a restaurant within walking distance on the same street, and an outlet mall just a short walk beyond that.