I've read many posts of users disappointed by their Quarks due to the loose threads and preflash, its difficult to recommend because of this. I would really like to get the Quark AA XPG, but they have to fix these things first.
Eagletac has a reputation for driving their LEDs hard, prices that beat their competition, great quality lights, lifetime warranty and great customer service. I am definitely in the market for a single AA EDC, there is no way I am making up my mind until I see what eagletac fields.
I am far from an Eagletac fanboy, I don't have a single one of their lights. But their reputation here tells me that they should be considered in any conversation which mentions 2xcr123, AA, 2xAAs.