Gravity Dropper still seems to be the most reliable, and is certainly the most servicable. Snap a reverb hose or mount and you'll find it relatively hard to get parts or bodge it, break a GD cable and every bike shop in the world has the parts. It's also lighter, and available in 5 inch drop if you've got the right seat tube. Service it with a bit of kitchen roll, some allen keys and some grease.
But still,the Reverb's reliable enough to not worry too much, except in specific circumstances (the under-seat union's very allergic to some uplifts!) so though it's bad news if it fails, no reason to expect it will.
But frankly, I'd buy a KS before a Reverb... The old one comes in 6 jnch drop and is very solid and a little cheaper, and the Lev seems to be doing OK and has the better cable location. Not to mention that both are cable so have a lot of the advantages of the GD. KS really seem to have learned from their mistakes, they weren't very good at first but now I trust my i900 as much as my GD.