The best melee atma is Razed Ruins, the +critical damage and rate increase your damage beyond any other atma. Other good ones are Gnarled Horn, Apocalypse. There is some fitting of an atma to your job, if you have a good critical damage WS, if you don't have a good critical damage WS don't bother with Abyssea. If you die a lot, lol, Atma of the Apocalypse (Triple Attack and Reraise3 FTW). Most people equip Razed Ruins, Gnarled Horn. There's also VV (Voracious Violet STR+Superior, Double Attck+Major, Regain+Major).
For jobs with a critical hit WS, the most powerful atma combination is Razed Ruins + Sanguine Scythe + Apocalypse. Sanguine Scythe could be replaced with Voracious Violet if you know you won't be engaged all the time - the longer you disengage the more the Regain will push VV ahead.