This is my opinion only, other peoples experience may be different. A 16' door would allow you to park two vehicles in provided you have enough depth and width on each side to angle them slightly. Thats how I would do it so you can open the doors on each vehicle. Maybe an 18' and a 10' would...
On the 10' door... I have a 10' and 16' door on the gable end of my barn (32' wide). I am not a fan of the 10' door. I use that side for my F250 and although there is enough room, it is very tight backing in. I only have about 3 inches clearance on each mirror without folding them in. If you...