So i've seen a few guide's on where to use a Potion of Luck . So being out in Kunlai summit for instance, or others used to be on the wall farming Mantid * before the hotfix *. So i have decided after a little legwork and watching the average respawn timers. It apears that the following mob: Gulp Frog 

Seem's to be the most ideal for using your luck potion and farm the hell outta them. if combined with Chi-Ji's Hopet it makes downtime next to none, Assuming your the only one killing the frogs So here is my summary after 1hr of farming in this location with an active potion up.

• 200 windwool cloth ( inside plundered treasure chest )
• 21 mote's of harmony
• several green's
• the odd timeless epic
• Alot of white and black trillium ore ( inside plundered treasure chest )
• and 150g in change

* not including the timeless coins or lesser coins of fortune *