CR123 lights certainly run the gamut in terms of size and features. Thus far I've yet to see my "ideal" single CR123 based light.
The HDS/Novatac lights come as close as anything save for their relatively large size given the cell size (and the Ra lights are even larger...).
Many would likely say the McGizmo's lights are the best but they, like the Novatacs, aren't Surefire L1 size but still are relatively large although bullet proof (and not that feature laden but of course what they do have is based upon a very proven design).
The EX10 is a neat light - definitely smaller than the HDS/Novatac lights - with useful features. But the piston drive is finicky when it comes to lubrication and maintenance, and the UI while cool, drives me batty with the lack of memory of the user level.
The LF3XT is another excellent light - almost as flexible and in some ways more flexible than the Novatac, with the compact user interface being similar to the EX10 except it remember the last mode. It's knock, such as they are, to me are twofold. While smaller, primarily in diameter, than the Novatac the LF3XT is only slightly smaller and definitely bigger than the EX10. And the original tailcap is somewhat sharp and less than finger friendly.
The EZ123 is small, quite small actually, almost the same size as my Peak McKinley key ring body which I thought was about as small (pocket body excepted) as you'd likely find in a single CR123 based light. It has a lot going for it in terms of RCR123 support and overall solid build quality. For a two stage light the levels are reasonably well selected - low is a solid utility level around the 20ish lumens out the front (compared to my Novatac) which is sufficient for most uses, and high is screamingly bright (although it really is more of a burst mode - you wouldn't want to use it for long given the high level and small mass). The cons, such as they are, are that the foam ring is not well designed - I cut the one on mine in half and it works MUCH better. The OEM ring is just too thick and made from too dense a material to condense properly in order to get to high. Some say that the amount of rotation needed to get to high is too much although it is about the same as a CR2 Ion and the Lunasol 27 no one complains about those lights (I imagine the Aeon and Nautilus are similar as well). At the price point, assuming you tinker with the foam ring, it is a very solid contender for pocket carry. I prefer a three level (or more) light overall - but the EZ123 is pretty nice and is competeing, somewhat, with the LF3XT and Novatac for daily EDC purposes.
There are, of course, a ton of other choices, some of which aren't as compelling to me but might be for others. Peak has some excellent and small single stage CR123 based lights, the Atlantic, Caribbean, Glacier Bay and Meditteranean are well built and rock solid, and generally small, if not feature laden. I expect that the Nautilus would be a strong contender but the titanium model is too expensive for me and the aluminum models are no longer made and difficult to find - and for the price while they are almost certainly more precisely made than the EZ123 (if my experience with the CR2 Ion is any indication) I'm not sure worth the price difference. The Nautilus may be as small or smaller than the EZ123. The Bitz has some followers and looks pretty small - I'm just not a fan of the twisty on/off interface. And lastly, the Arc6 is smaller than the McGizmo lights and the Novatac, but shares the piston drive/kilroy mechanism and it's reliability, and is programmable.
Pick your poison, so to speak!
