Trying to decide who to uncap next, as I have another mem 2 crystal.
Some recommendations on units to max even if you don't have one of their relics:
Ramza -- even without shout or tailwind, he's by far the strongest support 5 character. Best atk stat, wide range of equipment, and a very diverse skillset on top of support 5. His final record materia is also excellent (+50% soulbreak fillrate).
Vaan -- Similiar to Ramza, Vaan has support 4, along with excellent stats and equipment selection. Most teams generally want a support 5 for fullbreak and a breakdown, and a support 4 for one or both of the other breakdowns. Vaan can fill that roll easily. Also has thief 5 for thief's raid, but until his third level break, he can't break 170 speed except in FF12 realms or under burst mode.
Agrias -- A paladin unit that can bring protect or shell + a dps move. She also has one of the highest attack values in the game, along with combat 5, knight 5, and spellblade 4, so she can equip a huge range of very potent dps skills.
Celes -- She has excellent all around stats at level 80. She's by default a spellblade 5 (and next month knight 5), but something overlooked is that Celes can double as a pure black mage. She only has like 12 less magic score at level 80 compared to most of the mages, and she has black 4, along with full access to all mage equipment options. If you stick her in the back row with a rod, mage hat, a magic accessory, and some -ja spells, she can easily play pure mage at almost full power, with the benefit of being incredibly tanky. Eventually you may as well use a "real" mage, but early I had great benefit from a unit that could pull double duty on fights like that when I only had a small number of units leveled when MC2's were very scarce. Best spellblade dps record materia too.