I'm finding that the more items you need for a quest, the higher the drop rate. I know, it's crazy, right? Anyways I've been avoiding the ones that only require 3-5 drops, except when they lead to a good chain. When you go to a new quest hub, do some research and find out what the quest chains are like. Some collection quests are the first in a long line of NON-collection quests. Some are first in a long line of MORE collection quests.

Examples:

Lurielle (http://www.wowhead.com/?npc=24117) Her first quest is to collect 15 items. However, they're 100% drop, and then you get 7 really easy kill/use item quests!

Hidetrader Jun'ik (http://www.wowhead.com/?npc=27037#starts) Do all his quests, then you get to do the Conquest Pit quests from Grennix Shivwiggle (http://www.wowhead.com/?npc=27719)