Actually, my understanding is that a jam-cleat is a third animal altogether.
Its basically a standard horned cleat, but one horn forms a "V" with the
base, so you can jam the line in there for taking the bulk of the load off
before tieing off the rest of the line. I use them with my halyards, and am
reasonably happy with them. They're not particularly fast, but they work
well.
So we got:
Cam cleats (I use these on my sheets)
Jam cleats (described above)
clutches (I don't own any)
and lets not forget Clam-cleats. Very fast, efficient in the space they use,
and strong if sized properly for the line. I use these on my reefing lines
and my boom downhaul (that saves me lots of setup time).