The group to farm partially depends on your class. And how much effort you want to put in. Southern Felwood mobs are so low level that you can clear the entire village before respawns and drop mageweave. North Felwood is a lot of big packs of mobs so being an AoE class is helpful. I'm a Druid and I only farm winterspring because you make way more money. You can get firewaters which you can sell for 3-4g on raid days, and if you do the cache of mauri quest you can collect winterfall eko which you can either use for raid DPS or auction for around 80s-1g. I'm not rich rich but between my leatherworking and selling eko and firewater I'm doing real good. One time I put three stacks of fire water on the AH and three stacks of eko over night and woke up to like 140g which was a great feeling.
It can sometimes be hard to monopolize the winterfall king who spawns every 6-8 mins after his last death, but he drops a guaranteed firewater and has green-purple drops occasionally as well. What I do is I solo the king and his minions and start the stop watch and run around killing furbolgs. When it's getting close to 6 mins I head back to the king cave. I'm also grinding Rep so 25 Rep from king is great. Lastly, every 24 hours grizzle snowpaw will spawn near the cave entrance and so if you catch him that's a guaranteed high level green. All the high level greens can disenchant into Greater Eternal Essence which are worth a fortune.
