None. Keep your money and level the class/job. You will learn better how to use it as you level. But, if you are insistent on it I would do one of the dps classes/jobs. Tanks and healers have near instant queues outside of PoTD, so are a lot easier to level without jump potions. Dps it would be PoTD or pvp only as othet dungeons would be long queues.