Right now I have an AM that can 2-hit Petri/skele and 1-hit everything else, as well as an HS Mule. Is the best option to continue leeching myself? At what level, or point, will I have a better alternative? The character in question is a level 120 bucc with int gear and very low base int, so it can train/boss (at least, in how it can handle Manon/Griffey/HH) decently well.
Obviously at 135 you'll be able to zak/krex which will be way faster than leeching or grinding. Unfortunately, I suspect that leeching is faster than grinding, but you can always just spend 15-30 minutes grinding to see if it actually is. Grinding locations would probably be skeles / petris, tot, bigfoots, or hh. If you can, party to reduce the monotony.
Can also recommend himes, especially with the help of another priest. But usually, leeching would still be a better option. Btw, do you have an IL or FP? Depending on the class, you might be able to 1h certain maps in ToT. I remember leeching on Obv1 with my AM I/L when i wasnt able to 100% 1h petris. But, well, you'll need a bish as well to get HS in there.