I’ve owned a Gravity Dropper Turbo, a Specialized Command Post and a Reverb. None of them were cheap, but they were all pretty good. I can’t really say that one was better than the others, they were just good in different ways.
The Gravity Dropper is crude, ugly and not much more than a few springs and a pin. But that’s its strength really. You can strip it down on the trail (most jobs don’t even require tools). Every little bit is available as a spare (e.g. from CRC) for a decent price and you can basically keep it running as long as you want with just a few basic tools. It has three positions and the remote uses a standard gear cable. It’s the one I’d pick if I wanted to spend days in the wilderness and probably has the lowest total cost of ownership.
The Specialized Command Post is a bit more refined. The physical spring is replaced by an air spring, with a smoother action. The pin and hole arrangement is replaced by a more sophisticated collet mechanism. It looks a lot better than the Gravity Dropper and is more refined in use. It’s not as easy to strip down on the trail, but you can still do all the maintenance in the shed with basic hand tools. It’s still a three position post with the remote using a standard gear cable. It’s an ideal compromise between the crude Gravity Dropper and the fancy Reverb.
With the Reverb we move up another notch in sophistication and complexity. The cable remote is now replaced by a hydraulic line, it can be set at any height you like and even the return rate can be controlled from the remote. When it works it’s a delight to use. You can find yourself pressing the button just to marvel at the smooth action. The hydraulic remote is much more consistent in use than the cable operated ones, which can get clogged up and deteriorate as the cable gets sticky. But it’s harder to maintain and spare parts (e.g. the delicate remote button) are expensive. Bleeding can easily be done at home but probably not on the trail (unless you want to carry syringes and spare oil). For more thorough maintenance you may even decide to send it off to a professional. It’s my favourite of the three in use, but is also the only one that has ever failed badly enough that I’ve had to cut a ride short.
So, as usual, you pays your money and you takes your choice.