I tow two different RV trailers with my F-350. One is an approx. 19.5' trailer (7,000# gvw)with an Avion camper on it and the other is a 34' Avion triple axle trailer. Both tow great, but the longer trailer is easier to back up and would handle better in quick turns because it is lower to the ground. The long trailer is definitely easier to back up since the coupler to axle distance is more than on the 19.5' trailer. The short trailer is easier to get off the paved road since it sets higher and has a much shorter overhang and is only one axle so it doesn't have any tire skid issues in a tight turn. It has approx. 15" of ground clearance which means it doesn't get hung up going out of steep driveways. :)
If you are worried about the towing difference in a couple of feet, at those longer lengths, DON'T. You will never be able to tell the difference.