imo the easiest and most efficient way to make gold, is of course mining/herbing.
When you mine/herb and sell, there is no risk, no time invested and no complicated alt switching, all u do is farm, post, profit.
Raw materials might not be the most lucrative but, if you bot, time is obviously precious to you, otherwise you would farm yourself.
so, what i do is just AH my raw goods.
i dont make 20k a day but i make like 6-7k per day on a level 81 farmer in uldum.
Say what you wish, i tried it all and this is the only thing that worked well FOR ME.
but of course if you can spend the time babysitting your professionbuddy bot as it DE's hundreds and hundreds of items over a few hours then go for it you might make more money that way