I’ve had 4, because I’m a magpie.
Gravity Dropper- bought this already well used, used it nonstop for a couple of years, never had a problem with it that couldn’t be fixed in 2 minutes with basic tools. It had a few replacement parts- bushings and seals- but trivial really. More reliable, on average, than non-dropper seatposts I’ve had 😉
KS i900- got this not so long after, it needs a little more TLC than the GD but it’s been just as reliable. Original cable was crap though. Still using this, it’s ace and continues to be ace.
KS i950- didn’t work out of the box, went back on warranty and got fixed (though Superstar blamed me for it- they told me how to fix the problem, I did what they suggested, they said I’d caused the problem while fixing it, and then sent it back the first time still broken). This one’s also had a new oil shaft, which funnilly enough just broke again so that was replaced on warranty. But not expensive to service. Not perfect but more than good enough- as reliable as forks.
Reverb Stealth- haven’t had this long. Feels better made but the lever’s the worst of the lot and it’s just overcomplicated. I’ll cry actual mantears if I ever have to buy a replacement lever at £1000000 each. Wish I’d bought a Lev tbh but it was pretty cheap.