My vote is for the Eagletac T20C2 Mkii with the XM-L T6 720 lumen module. In my opinion the Eagletac feels a little more substantial in the hand than the Zebralight SC600.
I find the Eagletac T20C2 Mkii UI is easy to use, the light is solid and well made, comes with loads of extras, user upgradable modules, runs on CR123a primaries if needed and the beam is beautiful.
Last week on the same hunt for the best/brightest 18650 light I purchased the SC600 and the Eagletac T20C2 Mkii...They are both very nice lights, but I sold the SC600 and am loving my T20C2 Mkii.
I still love my Zebralight SC51w and H51fw, but in the 18650 category I prefer the Eagletac.