Welcome to playing, then!
Um. There’s your actual question, and then there’s all the stuff around it, that you’re not asking about. The stuff that either you already know, or you don’t know you should know.
There is a lot more gold in trading than in farming. But if you enjoy farming, then that’s wonderful.
But what you will enjoy will depend on how you enjoy your class, and that is something you will not know, for any class, until you try it.
On paper, the best farming class is Druid. Instant flight form, long-range pulls, good mobility, any amount of AoE, ability to herb without dismounting, stealth if you want to bypass things, Bear form to sit there and kill as much as you can pull - at long range. Guardian spec to farm current content. Druid has got it all.
That doesn’t mean you will enjoy Druid. It is just the most complete class, with the largest set of tools.
I agree that Warlock AoE is not wonderful for farming. Rain of Fire is rather clunky. Affliction spec has lots of instant DoTs for ranged pulling, but it’s not so effective at killing mobs in a mass.
Hunter has perfectly good AoE for a couple of blasts, but it is limited by Focus; you can’t just keep grinding out AoE spells - you have to stop and regain Focus before you can cast more than 2 or 3 AoEs.
Demon Hunter has great mobility, and its AoE is reasonable - not infinite, but reasonable. The one weakness of DH here is its ability to pull from a distance. Throw Glaive has a cooldown, which means that unlike almost any genuine ranged puller, you can’t just rotate through a series of distant mobs and instantly pull each one.
I have a Monk, but don’t play it much. Its Roll makes for nice mobility. Like the Hunter, it does have to alternate AoE (Spinning Crane Kick/Crackling Jade Lightning) with non-AoE abilities to recover.
You can make any of them work, depending on the type of farming you’re doing. If you’re going to spend a couple of hours a day at it, you REALLY want to enjoy the class you’re playing! A 10% increase in farming efficiency does not make up for feeling miserable at having to log in to grind out work.
I wish I could communicate better how each one is to play, but everybody has to try it for themselves, to see how YOU feel when playing it.
The patron saint of WoW farming on YouTube is Studen Albatroz. I actually like watching him occasionally - he genuinely seems to enjoy all the different types of farming. It’s nice to see.
But for serious gold-making, you want to get the addon TradeSkillMaster (TSM) and study up on the markets on your realm, and how best to use TSM to maximise your throughput. You will be reading the WoW Economy Reddit https://old.reddit.com/r/woweconomy/ as your daily news. And, of course, you want to be on one of the large realms, with a solid raiding population, and you want to be there on Wednesday night, to catch the crowds before and after the raids. Kazzak, as Horde, does qualify as an excellent realm to make gold on.
If you have any more questions, or want more detail, do please ask!