Rotten Hallow

All the quest NPCs are located outside the gates of Stormwind

It works well if you have someone from a guild with mass summon already there.

I made a thousand gold when I summoned a group of 10, charging each 100g.

A Time to Gain and Clean Up Stormwind are pretty straightforward as both quests can be done right in SW.

Stink Bombs Away! is also basic as you only have to speak to an NPC with the questgivers and you'll ported to Undercity to complete the quest.

A Time to Lose is where things get irritating as the flight to UC is long. However, there are a couple options to speed that up.

1. Take the zepplin in Grom'gol. If you have a flying mount, you can land on top of the balloon on the zepplin to avoid aggroing the guards on the zep. This is also a speedy way to get over to Durotar if you want to find Horde for Check Your Head.
2. As Emaziz states in A Time to Lose comments, you can just log out while on the broom in UC for Stink Bombs Away!. This will port you to the graveyard near Scarlet Monastary.

For your return trip, you can take the zepplin back, or just hearth.