I'd honestly upgrade with these options in mind.
MH: Garuda's Gaze, Giantsgall Longsword, Mog Blade, Lieutenant's Weapon, Sergeant's Weapon (Ifrit's Decent but it's the lowest on the End Game Weaponry)
OH: Thormoen's Purpose / Vintage Kite Shield +1 (Def Meld)
Helm: Cobalt/Sentinels Celata (MND Meld) (Try for a 30 Minimum at least)
Body: Cobalt Cuirass (VIT or Def Meld, your pick) (Aim for 30+ as well)
Gloves: Cobalt/Sentinel's Gauntlets (STR Meld) (Again aim for 30+)
Legs: Militia Trousers / Felt Trousers (STR/VIT Meld) (Try to get at least 15 STR/VIT)
Feet: Sentinel's/Cobalt Sabatons (Meld w/e you want, feet materia options are horrible)
Waist: Cobalt/Sentinel's Plate Belt (Aim for 40+ Enmity)
And upgrade to the best undies and undershirt you can find or get made. A few def is a few def no matter how you look at it.
Accessories:
Ear: Stonewall Earrings / Raven's Earring
Neck: Militia Choker / Explorer's Choker
Wrist: Coral Armillae / Raptorskin Bracelet
Rings: Rubellite Ring +1 x2 / Electrum Ring +1 x2
Negative, defense only impacts physical damage, VIT however affects all non-DoT damage taken. It's actually a toss up either way tbh, VIT doesn't quite benefit mitigation as well as straight Defense, but it offers magical resistance in return and boosts your Enhancement Magic Potency (which actually scales pretty good in this game) making Stoneskin/Protect and other magic buffs stronger in turn.