I find farming to be the fastest for me. During the duping era, i could farm out 2 per day on average. Now that duping is patched, ammy's are 4 times more expensive. So on average i can farm out 1 every couple days at the most.
Right now i am working on having 100+ of every pot stored up though, so i have not been adding to my ammy pile for a while. But the price of Ammy is still floating around 4 life.