There are actually three unmentioned types of compressors. There is an internal claw-and-fork style, which uses a thick fork on the upper end instead of claws. It's made by OTC and is much sturdier than the normal internal claw type compressors. This is the type I used recently when I did my front end work.

There is an internal plate style compressor that's ideal for Mustangs. One plate sits on top of the shock tower, the other goes inside of the coil while you tighten a threaded rod to compress the two. This style is very, very stable, and is what I'd recommend using if you can find one. I've used it once before and it worked out great. Catch is, they're very expensive if you want to buy one.

The third style is an external fork/hook deal. It's basically a large pair of forks with hooks on the end linked together by a hinge on the end and a bolt in the middle. As you tighten the bolt, the forks compress the spring. This type should also work very well, but they're rare and expensive, just like the plate-style compressors.