I have done a good deal of grinding in Cassiopia Hollow on crabs, and I have to say, CRABS SUCK. All you casters out there may disagree, but from a melee and tank standpoint Island Crabs are terrible. Even if we manage to get 3-400 SP, it is almost never consistent, and the crabs take way too long. They have ridiculous defense, their little curl-up-into-an-impenetrable-ball move adds a good 10 seconds to every fight, and because SP gain is proportional to the amount of damage you do, I only wind up getting 15-25 points per regular hit, and maaaybe 100-150 on the occasional Weapon Skill SP gain. I can get more SP fighting cassiopia's during party down time then I can from crabs. We have to find alternate mobs to fight. I know there are dungeons that parallel Cassi Hollow in the other regions, but from the ones that I have been to, I have not seen much. If you have any knowledge of a good camp for parties of 4+ people level 20-25, or 25-30, please post them here. Any mobs that are softer than those crabs that come up as blue for a 4 person party in those level ranges is acceptable.
Death by Asuran Fists.