The youtube video of the Nitecore EX10 is what got me into the whole high power flashlight thing; I saw the video and immediately ordered one. That was almost 2 years ago, and I've never had a problem with it. (I did clean the excess lube off the piston early on, though.) I liked it so much, I bought 2 more, one for my dad and one for my brother. Neither recipient is a "flashaholic", but both work in fields that regularly require bright personal lighting, and both of them have EDC'd their EX10s for over a year now (some pretty hard use, too) with no problems. I would heartily recommend any of the SmartPD lights (EX10, D10, D20) if they still made them. :shakehead
On the other hand, I decided I wanted something a little different in AA, so I picked up a Nitecore NDI and have had nothing but trouble with it. The "rapid head twist" interface just doesn't work right and I can never get it to do what I want, when I want. I even sent it back for repair, but the seller said there was nothing wrong with it and shipped it back to me. It's got a beautiful beam, but I never EDC it because I have other lights (the EX10, for instance) that I trust to work when I need them to, and I can't say that about this NDI. I have seen other threads complaining of the same issue, so I'm not the only one. I would not recommend either the NDI or the NEX, as both use the same interface.
The only experience I have with Dereelight is with their Q5 P60 drop-ins, but again, I liked the first one so much I bought two more, and none of the three have ever missed a beat. All three are currently residing in Surefire hosts, and all three get subjected to some hard use / mild abuse, but I have not seen any problems from any of them. The Dereelight UI is the usual boring 3-mode w/ memory, but it certainly gets the job done. If you're looking at tiny lights, then the C2H now has an optional AA extension tube (omnivorous lights are good). Also, the replaceable pill system is brilliant for upgrades or tint changes (and is used with all of their lights).