Here's my take with my background of many years in "campus" law enforcement, where bike theft is one of our constant problems. Cables are simply not as good as U-locks. Most all the bikes we have stolen are "secured" with cables.
Having cut quite a few of these myself (we sometimes have to seize bikes, or remove them from improper parking area, or just cut it loose because junior forgot the combination...)
A standard 16" bolt cutter, the type favored by bike theives, will open to about 1/2". Provided the cutter is sharp and well-adjusted, it will rather quickly cut anything that will fit inside the jaws.
So, the big, thick braided cables are better. They can be defeated, but it takes time. The theif has to "nibble" through the cable, which takes time and attracts attention.
The advantage of cables is that if the bolt cutter is not sharp and well-adjusted, they just sort of "mash" together and nothing gets cut.
So, if you must use a cable, get the widest, thickest one you can find.