I've heard people give different playing orders for the quest packs, but I think the general consensus is:
Main System
Kellar's Keep
Return of the Witch Lord
Against the Ogre Horde
Wizards of Morcar/Zargon
BQP
EQP
Dark Company
The first five have clues to the order found in various info. Agin's Inn(RIP) had a nice layout of this. It can still possibly be found at this link via the wonderful wayback machine.
Post Transfer from Old Forum - Original Post Date: Tuesday January 15th, 2008 12:53am