After reading what others have posted I have to say I use all or a combination of them all. My trailer is able to be jackknifed and a cable lock runs through the trailer and bike. I often times carry two locks one is a cable lock with a U-lock, and the other is a cable lock. One keyed one combo.
If I am not going to be long and the area has nothing to lock to I just lock it all together in an inconvenient manner so that if you tried to carry it off you could not really do it easily. I have left a bike for two hours like this in an area that people would know I am gone for at least an hour.
I try to always lock them together while they are attached. There are some extenuating circumstances they have to be unhitched.