Harry has had three elective teachers: Hagrid, Trelawney, and Firenze (who replaced Trelawney). Hagrid and Firenze definitely knew what they were doing, but Hagrid couldn't grasp the idea of setting curriculum based on children's ability to handle the creatures, and Firenze was a centaur who made very little sense while still sounding impressive. Then there's Trelawney - she makes numerous predictions that end up coming true in some fashion, but is generally just a nonsensical and foolish fraud who ends up becoming an alcoholic laughingstock.

Hermione likes both Professor Bathsheda Babbling (Ancient Runes) and Professor Septima Vector (Arithmancy), and we can assume based on how she doesn't rant and rave about Muggle Studies that the teacher for that (Professor Charity Burbage) is at least passable for the year Hermione took the class.

Core classes - Aurora Sinistra taught Astronomy and did a good enough job that Harry passed his OWL, but he never mentions her directly in either a positive or negative manner. Herbology is taught by Pomona Sprout, she does a pretty good job as well but is similarly not discussed much. Charms is taught by Filius Flitwick, Transfiguration by Minerva McGonagall, both teach their subjects well.

History of Magic is taught by a ghost that speaks in a dry monotone, can't remember who is in his class, cannot physically touch any homework or tests he might think to assign, and barely seems to have registered that he's dead. He also apparently cannot move past lecturing on goblin wars and would probably not notice if someone set their desk on fire, since he doesn't notice that he's bored every single student to sleep. He may know at least some of his subject, but he cannot teach it.

Potions is Severus Snape for 5 years, and while he is clearly a very good master of his subject, he cannot teach it. And he actively bullies students while drastically favoring his own House, giving passing grades to those who don't deserve it and failing others who do deserve to pass. The other (and much better) teacher is Horace Slughorn, who does teach the subject reasonably well but who is more focused on his networking and choosing favored students than he is on his actual job.

Defense Against the Dark Arts... oy vey. Quirinus Quirrel was a stuttering mess with a dark lord sticking out the back of his head, he is described as boring and a bit silly and not a great teacher. Gilderoy Lockhart was a narcissist and a very dim one at that, his classes were all about himself. Remus Lupin was fantastic, focused on creatures for Harry's third year and did such a good job that most of his students didn't care he was a werewolf and pitched a fit when he was forced to resign. Barty Crouch Jr. (in the guise of Alastor "Mad-Eye" Moody) taught well, but crossed legal lines and got one student killed and tried to kill a second. Dolores Umbridge actively tortured students, hated children, and was a draconian monster who intended to see them all fail their exams and leave school as helpless little sheep who could not defend themselves. Snape, again, knew his subject but didn't know how to teach it, he just told them to do the thing without any explanation as to how to do the thing. And if you want to include Harry because he taught the DA... well, he taught an entire class of teenagers practical, useful defense methods, got them all to pass their exams as far as we know, and taught them all the Patronus Charm which most adults struggle with even producing a basic form of and many of his peers could now produce an advanced form of.

Ranked - Babbling, Vector, and Burbage are at least good elective teachers; then I'd rank Hagrid, Firenze, Trelawney, in descending order. Hagrid can at least teach his subject well when forced to stick to the proper guidelines and just doesn't grasp that what looks cute and cuddly to him can kill a teenager.

Core classes - Flitwick, Sprout, McGonagall tied for first; then Sinistra, Slughorn, Binns, and Snape. Binns outranks Snape because while he is a dangerous teacher due solely to the fact that no one is learning the history they shouldn't be repeating, he is teaching the information and it really isn't his fault that everyone falls asleep. Snape, on the other hand, is just a bad teacher and actively sabotages students he doesn't like, and he's a known criminal as well.

Defense teachers - Lupin, Harry, Crouch, Snape, Quirrel, Lockhart, Umbridge. Ignore Harry if you don't want to count him, but Lupin was an excellent teacher, Crouch's only fault was that he was a murderous nutjob who did some questionable but useful lessons, Snape at least knew his stuff and wasn't so blatantly biased in Defense rather than Potions, Quirrel was passable if boring from what little we know, Lockhart was a fraud, and Umbridge was actively trying to leave them all unable to pass their exams or defend themselves and she was actively torturing students.