Necro! (k not really). Mostly wanted to mention mastering Necromancer won't force the Undeath trait on you. Just like the Berserker's Berserk, Freelancer/Mime won't copy those harmful traits. But then I thought about it. Did you know you also you gain stat increases of the various jobs? Only the highest bonus applies though.
Here are the prime classes to master.
Monk: Counter, highest Strength increase (+26) & highest Stamina increase (+26).
Thief: Highest Agility increase (+16).
Summoner: Highest Magic increase (+33).
Ninja: for Dual Wield, lets you attack twice per attack command.
Ranger: for Rapid Fire, sends your character to attack four random targets, Dual Wield means eight attacks in one go!
Mystic Knight: for !Spellblade, used to add in Flare or w/e to your attack to help insure you hit cap if you didn't already.
Blue Mage !Blue Magic, simply superior to wasting command slots on White & Black magic.
Keep that Bloodsword too. It ignores Rapid Fire's damage penalty and benefit's from Rapid Fire's near auto hit chance. It's so good a couple of none undead bosses are treated as undead just to give you a few surprises. There is also a blade (think it's one of the legendary) that attacks twice but offers little towards base damage, Spellblade it and though dual wield triple attack up some death.
