I've tried a few ...you can read about it here. I currently have the RockShox Reverb (2012 version) and it's holding up well. I have no regrets getting it.
Fox is coming out with one sometime this year, I would wait for a fox product over all the other ones thaat seem to always have problems after a couple months.
I bought the Specialized.No problems,smooth action with no side wiggle.I liked the idea that the post locks into position so if the seals fail it will still work in the extended position.
I've had a K&S i900R for about 1 1/2 yrs. Absolutely love this post but did have to send it back for svc once (started to sink at full extension after about 1 yr). Quick turnaround of 1 wk with no charge. I definitely highly recommend the remote release. Also the i900R has a 32mm setback that works well for me.
Have heard many not too good reports about CB Joplin. Even the mags that advertise them slammed 'em.