NH-U14S is very good.
I think Cryorig and Noctua are a couple of the best because they use thumb screws and nuts Phanteks also uses thumb screws and nuts and are easy to use as long as the crossbar is attached to mount before final tightening of mount (to be sure crossbar screws line up with their holes in sidebars). Thermalright are good but just use small screws so a magnetic screwdriver is required, and their crossbar is not attached to cooler base so not as easy to install..
The 6600K does not need a big cooler. The Cryorig H5 would be good. Maybe H7 too, but I can't remember mounting it (only mounted for testing long ago).. @ciarlatano
needs to remind me, but I'm sure he's sleeping right now.. I remember it does not use a through motherboard mount. The only down side to Cryorig install is user needs to know where to position cooler so it's screws line up with mount and start. It's not hard to do, but needs to be kept in mind .. and don't over-tighten the screws. The thread in so easy some people have thought they were not tight and broke them trying to make them tighter.
On a side note.
Many screws / nuts are now Pozidriv not Philips, and require the use of a Pozidriv bit. Phillips bits strip Pozidriv screw / nuts rather quickly and Pozidriv bits strip Phillips screw / nuts even faster. They look almost the same, but the 'X' of a Phillips is tapered while Pozidriv is not. Simply put they are not compatible .. not at all.
You can identify Pozidriv screws / nuts by the little dash marks between the slots
I know, it's off topic .. Edited by doyll - 6/15/16 at 11:51pm