I prefer to use twine in the woods, because its biodegradable, thinner and cheaper.

In the mountains i'm all about 5 and 6mm prussik cord, because it can take body weight and in the climbing world they are pretty much to most versatile piece of equipment you can get.

For DIYing just any proper cord. Depending on what kind of application some smooth or rougher cord. (paracord can be a slippery).