After spending several weeks trying to work out what's the best case for me, I've been using the Spigen Liquid Crystal almost permanently for over a month now. It's been great. It essentially fits all the following features I look for:
1. Has to be light ("thin fit" etc) - anything thicker/heavier than the Spigen Rugged Armor is definitely excluded - it's thin enough so it doesn't feel like it adds any significant weight, but thick enough so that it feels like it provides some scratch protection etc
2. Has to be grippy enough for easy one-handed use - probably as good as it gets. If it was any grippier, it would be noticeably more difficult to slide in/out of one's pocket. Furthermore, there would be even more "fingerprinting" and "dust gathering". It's comfortably grippy enough for true one-handed use, which is such a convenient option to have in everyday life.
3. Not a fingerprint or dust magnet - as above, probably as good as it gets without being too slippery. For it to be less of a fingerprint/dust magnet, it would almost certainly need to lose some grippiness. So I think it strikes the perfect balance.
4. Can't be too restrictive with side swiping from edges of phone (to bring up swipe-in menus) - as I've previously mentioned, this is an issue with almost all cases with raised side lips. The exceptions are the cases which are usually very cheap (typically less than 5 dollars) which have barely any raised side lips. But these cheap cases tend to be quite fragile and tend not to have accurate cut-outs etc. With the Spigen Liquid Crystal case, bringing up any swipe-in menu is very easy once you know the technique (sort of a rotational-like swipe)
5. Power and volume buttons must be easily accessible (as similar feeling to without the case as possible). Any case that makes a louder click when pressing the buttons is effectively ruled out - actually makes a softer click when pressing the buttons, so that's rather amazing. The buttons still feel nice and tacky with good feedback despite this. As good as it gets really.