I couldn't stand any of them, but in order of total uselessness and boredom-inducement:
1. Service Meeting
This thing totally sucked. The only slightly useful part may have been the Announcements. Sometimes. After that, it went straight down the toilet with demos that seldom if ever portrayed reality, and awful round-table discussions that left the audience brain-dead.
2. Public Talk
45 minutes (used to be an hour!) of more mind-numbing sleep-inducement. If the speaker was anything less than scintillating, this thing was a total drag. Sometimes, a really good speaker could salvage it.
3. Theocratic School
The only thing that keeps this from being worse is that at least there's a variety of speakers, and the parts are generally short, so things seem to move along a bit. But, it's the worst of all the meetings to prepare for, and conducting this thing, which I did for several years, was a nightmare.
4. Watchtower Study
The only thing that saved this is that the audience got to participate. But all too often, answers droned on and on, and conductors kept up a snail's pace. And why read the paragraphs? This thing could be done in 30 minutes every week, just like it is during the CO's visit.
5. Book Study
This is the lesser evil only because it's the shortest meeting.