For me, I find hellhounds to be pretty fast for golds, along with the occasional clue scroll. Also giant rock crabs can be pretty fast for golds if you mage them. For greens, bloodvelds, but don't go out and collect greens. Crimsons are where the XP is at.. I find KBD (King black dragon) is very good if you find a nice duoing partner and find an ls world, you can easily get 20-25 kills per trip which is roughly 40-50 crims each per trip. Rock lobsters are fast, but very expensive. Waterfiends are faster than KBD but slower than rock lobs, and you can pull a slight profit. Blue charms - I don't know much, I don't collect blues on purpose.