Garmin GPS units with Lifetime Maps and Traffic (LMT models) are good at picking up CURRENT traffic delays.
I know of no GPS which routes around historical traffic delays.
I've not had any difficulty routing around major city centers, or construction areas, with a Garmin Auto GPS or a Rand McNally RV GPS
The key is to sit down with the GPS and a map the night before you travel. Let the GPS create the route to your destination. Then add waypoints to force the route to avoid the area you want to avoid.
The save that route as a multi-stop trip.
The Rand does allow me to set temporary and permanent exclusion areas. The problem is that if I set a permanent exclusion for downtown Boston, as I did, then the GPS is useless for tourism trips into that area.
I have two multi-stop trips saved in my GPS to avoid Austin, TX. I will select the multi-stop trip that takes me either east or west of Austin, then add my destination as a via point at the end of the trip.
Take the GPS out some slow evening and practice changing the default routing to better suit your needs.
With the Rand I find it easy to find truck stops along the preferred bypass route and set up hem as a waypoint. Then the GPS will not take me into the undesired area. Highway intersections can also work easily.
In April 2015 I had to travel from Colts Neck, NJ to Thomaston, CT which the GPS of course wanted me to go thru NYC.
I added the Pilot at Mahwah, NJ and the Pilot at Newburg, NY as waypoints and didn't come anywhere near NYC.
There are eleventy-eleven threads on this forum about the best way to avoid D.C., look them over, pick the route you want and set it up and n the GPS.