Although the concept of a grapple bucket is a good one, mine did not work out so well in practice. I ended up with an MDS rock bucket grapple, which while a very sturdy product, is simply too big for my tractor. Also, the grapple part of it is an after-thought that really isn't very useful because its "bite" is way too big (can't clamp down on a stack of sticks, etc.)
Being a newbie (when I got the setup), I let the dealer sell me what he had instead of what I wanted (an Anbo grapple). Although I did manage to use my MDS to drag a few downed trees, I could have just as easily (and a lot more cheaply) done this with chains. My problem was that the tractor was not plumbed for grapple hydraulics and I was afraid of putting those on myself, so I just handed the dealer a big wad of cash in exchange for an education.
I don't use the disc harrow or rear blade all that much, but since they are on loan from a neighbor who doesn't use them, this doesn't really count, now does it.
For that matter, now that I've cleared my orchard of trash trees, I no longer have a lot of use for the backhoe, but it sure was effective in tearing out an acre of thorn trees in short order. Besides, I might feel destructive once again some day, and I'd hate to be without it.
Most useful? Easy: the brush hog. Was going to use it tomorrow, but since we got a good rain tonight, that's going to have to wait.