I have rectangular unibrow that is sparse but with thick individual hairs that refuse to be waxed (rare to be offered brow waxing in India, so only ever tried that once); I get them threaded maybe once a year or so, to adjust shape, and then tweeze.
Rationale: I'm fussy and impatient. I refuse to wait to grow stubble long enough for threading every couple of weeks(!). I hate going to salons and beauty parlours almost as much as I love my dentist :-/ . I won't let anyone touch the top of my brows --- threading from the top looks... not natural enough for me!, plus they always try to gently curve my sharp angles, which I actually am rather fond of. And I like to push my eyebrows a little further apart than 'ideal' because it creates the illusion of pushing my close-together eyes apart.
So I guess I'd thread or wax if I had (1) more patience (2) thicker skin literally and figuratively (3) less stubborn hair follicles (4) greater sociability which allowed me to relax in a salon situation. As it is, my sensitive skin and I prefer tweezing because you can give up halfway without it looking weird --- I just pluck a few at a time per side, each day. And I much prefer the softer line (less 'precisely' drawn, if you like) that results.
If you prefer great neatness and have less time on your hands, waxing or threading seem to be better bets --- and of those, threading is more precise still.