For keys I would prefer a stainless steel light, it does not scratch as easily and scratches is not as visible.
The Klarus (like the ReVO) has a solid hole for mounting a splitring in.
I have done reviews of the Klarus lights and the previous generation of i3 (i.e. A3) and done some comparisons between them and other AAA lights on my website.
I've had a stainless steel Preon Revo on my keys for a couple of months now, it still looks like new, and gets a lot of use. Simple UI, the low it starts on is enough for dark adjusted eyes and the medium is good for lighting up footpaths etc. I would highly recommend it, but have no experience with the others you listed so can't say how it compares.
Cheers, Matt
I had a Revo and sent it back. Didn't like the way contact is made by crushing the battery and squidging a bit of foam.
The traditional system with a normal spring in the tailcap and contact ring at the head end works just fine in many other lights, including the i3, so I don't understand the ReVo design.