I will have to say having crossed both the CBBT and the Chesapeake Bay Bridge (Rt 50 near Annapolis), my choice would be the CBBT any day... The Bay Bridge (Rt 50) is very high off the water with pretty narrow lanes.
People get nervous driving cars across it let alone Big RV's! I crossed it a few weeks back with a colleague of mine in the car with me (not towing), and she just looked at me and talked the whole time... Got nervous when I took one hand off the wheel, and she was just the passenger.
Google Chesapeake Bay Bridge and look at some of the pics...
I have walked out to the middle of the Bridge at the Hoover Dam (there is a walkway to walk out and take pics of the dam). It is definitely higher than the Chesapeake Bay Bridge, scary from that perspective. Big difference is the lanes are more wide with shoulders... Not as scary as driving right next to the rail...