I heard both before going in for the Meridian. Purchased solely to use as a headphone amp, but am quite content using it in my stereo system, as well. My reasons are as follows:
1. Sound. This is very clear from the first few notes. Typically Meridian, music has a certain ease and smoothness to it. The AQ, on the other hand, while a tad more dynamic, lacked what one might refer to as 'finesse'.
2: Hirezability. A matter of choice really. The Explorer does 24/192 as opposed to AQ, which is limited at 24/96 (not sure if the new version does higher)
3. Build: Besides the subjective preference for aesthetics of the Explorer, I thought the Dragonfly was slightly clunky, jutting out directly from the USB port. Prefer the fact that the Explorer had its own cable.
4. Brand Value: Again, something rather personal. If I'm buying a source component for a certain amount of money, I'd rather spend my money on a trusted name in high-end systems like Meridian, rather than a cable manufacturer.
Hope this helps.