There's a lot of great design work here.

The one that's currently in the lead (by mjbmonetarymetals) is certainly amongst them, but in my opinion it doesn't really say anything about Quark to people who aren't already familiar with Quark.  And if you look at it objectively, disregarding the flashy binary backgrounds etc, the logo itself is a pretty simple rehash of what Quark already uses.

I like the boxxl design.  It has a "money" feel to it and It keeps the familiar quark symbol while introducing the 'Q' which may be important for people who are less familiar with Quark already.

I also really like barrysoetoro's design.  In my opinion it's by far the best conceptually thought out design and looks very clean and modern.

Either of these two designs add strong credibility to Quark's public image but as I only have one vote I selected barrysoetoro.