I think Dragonspire is longest for me. Several reasons would account for this...if you look at a typical battle in WC, it takes 2 pips to take out most non-bosses (example Death vs 235 health foe: one wand attack, then a ghoul). You get to Krok & Marley, you face two foes, but with a good spell and boosts, four rounds/foe, 8 rounds total. When you get to DS, it takes usually 6-8 pips to take out a common street foe (usually 1000+ health), but with increased power pips, takes about the same number of rounds as in the Krok-to-MS combats....but, while in Krok you may have to fight on average 4-6 foes per simple quest, in DS it is usually 10. Or a 50% increase per quest.
DS has longer and more difficult dungeons based on the level you are facing them.
My averages currently: WC to MS: 2 1/2 weeks GH: 1/2 week DS (to GM): 1 week . note, the above includes all side quests and crafting. . note 2: DS is a bit longer due to crafting quests.
I thought Marleybone was the quickest for me. I didn't do that one dungeon though, I kept getting hit with three spaztic wooden dolls running around attacking me. But I finished MarleyBone in 2 or 3 days. I'm only mid-way through mooshu right now, and it seems it'll be a bit longer than marleybone, but the longest for me so far was the second world.
