Most any site is going to exaggerate the elevation gain. The main problem is that the elevation calculations don't take into account the actual road. For instance, if you cross a bridge, the program assumes that you followed the contour instead of staying level on a bridge. Same thing where you went through a tunnel instead of going over the mountain. MMR, BRT, Bikely and the likes all sort of use the same data to make those computations - their smoothing algorithm usually is what makes the difference. The point here is that you need to compare route to route, not site to site.

RideWithGPS has done a great job so far. Hopefully, they don't get bored with it and keep things improving. As with many of these sites, the developers get something going, then get bored with it or just don't have the time to continually improve it. No offense to bikeroutetoaster, MapMyRide, bikejournal.com - they all make great stuff, but there really hasn't been any new features added in a while.