Quark vs. Zebralight - which one?

[readyme]

I am looking to get a new single cell AA light. I think I have narrowed it down to the 4Sevens Quark AA Tactical and the Zebralight H51 light. I realize they are different forms, but that is OK.
My question is, can somebody compare them in terms of brightness and run time (how efficient they are)?
I personally like the Quark Tactical UI better than Zebralight, but I keep hearing how everybody loves their ZL.

Thanks