In reply to mike123:
Reverbs are ones to avoid as they stop working in the cold and are susceptible to air getting past the seals resulting in them sitting into their travel between 0.5 - 1cm. They've been discontinued by SRAM (except the electric one)
In my opinion you're choosing between two...
Brand X if you can get hold of one (Wiggle/CRC who owned them recently went into administration and the brand/IP were bought by Mike Ashley - not sure if they are still being manufactured or not) - check the stack height you need as the section in the frame is longer than other posts (only an issue if you have a kinked seat tube) - I've had one on one of my bikes for just over 2 years and it's been flawless so far
One Up - these are slightly more expensive than the Brand X and just as reliable - these have one of the shortest stack heights of all the droppers so great if you have a kinked seat tube. I've had two so far the first was a 170mm V1 post which I ran for about 4 years - all it needed was to have the air chamber topped up every 9 months or so - sold it when I got a new bike - I currently have a 180mm V2 or v2.1 (can't remember which) it's about 18 months old and has been similarly good - it needs the occasional air top up - there is a V3 version which doesn't need an air top up
Both the above are easy to work on at home unlike the Fox Transfer which isn't home serviceable