Best prof = invest in a market you enjoy. Works every expansion with little farming involved. Get setup with bulk suppliers that sell to you cheap for instant gold. Keep them paid and they remain yours... And resell @ norm/high for mass profits. There are tons of people that enjoy farming and hate using the AH. So buy their stuff... Saves you from spamming trade chat also. You both walk away happy. (For those that frown at this method, welcome to the real world. People buy @ wholesale and sell to you @ retail everyday making them profits)
Use the other prof farm methods for when you get bored or just want some extra income / scenery change

Using that method has actually allowed myself/friends to enjoy the game without having to worry about being broke or farming endless hours!
(If farming with friends/family, then that is a different story and worth all time invested)
/cheers