Ultimate reliability, ease of repair/maintanence/getting parts/initial price the Gravity Dropper wins, hands down.
I have one GD Turbo that is 7-8 years old. A basic service once in a while is all they need. Older models (like mine) had a few issues which have since been addressed and fixed. Mine was upgraded to the newer bits, no problem since. The company is very good to work with if you have any issues.
I have one regular Reverb, and one Stealth model. Love both. If you have the option to do the Stealth, do it. DO NOT buy a used one, and try to make sure it's one of the newer versions.
Caveat: the Reverb requires more upkeep on a regular basis than some other posts. The nature of its functioning just makes it so. Newer ones are far less probelmatic than the initial runs. They have beefed up the connections, and fixed some seal issues. If you buy a newer version, you ought to be good to go. However, you still have to cut/bleed the system on install, and good functioning of the post is very incumbent on doing a very meticulous and good job with the bleeding. The functionality of it comes at the price of upkeep. I loooove mine with the right side remote run upside down on the left, with my brake lever and no front shifter. Out of harms way in a wreck, sane looking, perfectly placed to nail it quickly and easily with my thumb.
The Stealth model requires a bit more work on install (duh, just by its nature) but other than that, same deal. So long as you are okay with doing a bit more initial work, and paying attention to things, they're fine.
The only issues I've had are 1: when I pulled the line out of the remote end in a wreck. Popped it back on, and it worked (slowly) for the rest of the ride. A new barb and and bleed at home (15 minutes) had it good as new again. 2: the first one from the first run I bought was DOA. Returned. It's replacement worked great, then had sealing issues at the remote end. Once swapped to the newer replacement seals and hose barb ends, it's been good to go.
IMO, if buying ANY hydro system, pick up a seal and service kit when you buy the post, then you've got it if you need it, rather than having to order and wait.
The non-moving hose posts from KS and Crank Bros. sound to be duds, from numerous reviewers out in bicycle web-land. Hopefully they'll fix their issues as well. More options are good.
The Thompson looks great, but hasn't been out long enough for many reviews to come in. Hopefully it is as good as their regular posts. We just don't know about its long term reliability and service yet. To me, it and the Fox DOSS don't offer anything new to the market though.
I've also added a tough of grip tape to both mine. Also have on my shifter paddles - when it's so nasty humid here, things get slick even with good gloves.