That would depend on many things. The GW is usually a roll of the dice. I used to run from Newark to Boston daily and my rule was usually to go up US17 to I287, over the Tappan Zee Bridge and up I684, or up US17 to I87 (NY Thruway) to I84 and over the Newburgh Beacon Bridge, once school lets out. Even then it can be pretty crowded on a Friday afternoon. These routes are longer mileage wise but in most cases will save you a lot of time and headache.
Unless you are experienced at constantly merging with very aggressive traffic I would not suggest the GW with my motorhome. It can get very ugly.
You can get traffic reports every ten minutes on the 8's on 880 AM and on the 1's on 1010 AM for the entire NY/NJ metroplex. The traffic reports will usually lag the event being reported by 10-30 minutes. If the reporter says it's 10 minutes to the bridge, he means it's 10 minutes to the toll booth. It can still take as long as 20-45 minutes to cross the bridge. My other rule used to be that if the time to the toll booth was in excess of 20 minutes I'd be looking for an alternative route.
Good luck, be safe and enjoy the trip.