Well Mora's of course and I don't really like the snap on the retention strap of my SOG nw ranger, it's plastic, very bulky and it's a pain to do up, originally it wouldn't do up at all. I'd have to say ESEE knives as well, specifically the 3 and 4. When I first got them I thought the sheaths were great, they had good retention and with the molle backs attached the system seemed very secure but over time things have changed.
Both sheaths have loosened to the point of not retaining the knives well, the 4's sheath had the option to tighten it at least by putting a screw into the top hole of the sheath (there were some problems with that though because of the supplied hardware), the 3's sheath has no way of tightening it though so it's permanently loose now. The molle backs elasticated part slips off the top of the handle far too easily, if it's on my belt and I bump the sheath against something the flexability between the sheath and the backing causes it to pop right off. Maybe it wouldn't be such a problem with molle gear, I don't know. The retention strap is my main gripe with it though, I have no idea what they were thinking when they put velcro on it. The velcro has almost completely worn out on my 4's molle back causing it to come undone with the slightest touch, it also gets full of snow, grass and all sorts of things making it a pain to secure. Also I've found that since the same molle back is used for both the 3 and the 4 the one side of the retention strap is too long for the thinness of the 3's handle so that when I pull the tab over top of the other piece it has a tendency to push it over a little making it slightly loose (it's hard to explain). Now that tiny bit of looseness wouldn't normally be a problem except that it happens to make the retention strap wide enough for the whole knife including the guard to pass through it.
In theory the sheaths sound bomb proof but there seem to be some pretty big design flaws and with a little wear and tear they end up with horrible retention. I think if they added the slide lock they use on the 5 and LS to the sheaths of these knives and threw a snap on the retention strap (and sized them properly) they'd be way better, doubt that'll happen though.