Animal Caretakers, hands down. It doesn't do anything at all and yet I still get several ranger types in each immigration wave that have the skill. Just cause Mountainhome don't want them doesn't mean I want them either.
Next are the dissectors. Totally useless pair of occupations, but at least they can actually do something, even if it's a complete waste of time. Also glazers, only needed to make pottery watertight, which is never needed because all that stuff can already be made of stone and glass, and if there's good access to fire clay then stoneware is already watertight and more valuable to boot. Trappers are also near the bottom of the barrel.
They're followed by siege engineers. I've never really gotten around to using siege engines, because of the whole only hits things on the same z-level issue. And siege operators from what I hear start cancelling jobs when they see enemies which kind of make them less useful. Bowyers have them tied, only useful if I need to crank out a lot of crossbows and I have better access to wood than metal. Pump Operators aren't really that good either, since I have the skill on my entire melee militia for strength training. I don't need dedicated pumpers.
Which brings us to useless farmers. Beekeeping is mediocre, I'll eventually get around to having a single beekeeper, but that is only once all the essential industries are staffed properly and running smoothly. Waxworking simply gets enabled on my normal crafters. Pressing is kind of crap too, it seldom gets used. Milking, cheesemaking, shearing and spinning are moderately useful, but I combine those on a single dwarf since none of them have enough labor for a dwarf to specialize completely in them. Potash, lye and soap making also gets assigned to a single dwarf, since they're occasionally needed but are low-volume industries.
Just about everything else gets used in the fort.