Its sad that no one levels Goblin anymore, and I don't see why. They can spawn almost anywhere in the world, and they have an excellent specialty in aggro. It differ between magic and physical depending on what you spawn as, and it, like other beastman npc classes, has the 'Gil Dropper' trait so you always drop gil on defeat. You also get an immunity to charm, no more reduced experience due to those beastmasters.
And you can't forget their awesome abilities. The Dia line of spells will deal damage over time and lowers their defenses, ticking them off immensely, and Goblin Dice will tick them off with random status. If you spawn as certain NM, Saucepan will infuriate you foe by replacing their food effect. Last, but certainly not least, Bomb Toss has a chance to backfire, killing you and thus increasing your efficiency, and may attract PC Blue Mages who want to learn it to fight you. If they do have the Blue Mage class, make sure to use it just enough times that they keep killing you, but take a long time to learn it. It both infuriates them, and ensures max exp from getting killed.