AN, HOL, DTK, and UK are pretty fast. Especially AN...seems like every time I do that one, it's, "That's all?" Heh, heh...!
The 5 badge ones are probably more badges per time spent, though, when one factors in the time it takes to get a group together, on any given day. Personally, I like Gundrak, as long as everyone knows the "quirks" of the fights, it goes quickly, and has that extra badge.
As someone stated, it depends mostly on group dynamics, in the absence of over gearing.
-"Just like a buzzin' fly, I come into your life, I'll float away, like honey in the sun..."--Tim Buckley