Weapon
False Grecia: MATK+10%. MP Consumption +30%
Isurugi: MATK+12% MP Consumption + 25%
Dunkelis: MATK + 13%. MP Recovery -20%
Gerust: MATK +20%. Skill Delay +1 second
Beelzetor: MATK + 14%. MP Consumption +35%
Fiona: MATK +14%. Skill Delay -0.3 Second
Armor
Shojo: MATK +5%. Wind, Earth, Water, Light Magic + 5%
Moldus: MATK +14% (Use only if you have DEX 200+)
Additional:
Tarna: MATK +15%. Magic Power + 500
Ushilth: MATK +12%. Skill Delay -0.5 Sec
Special:
Mezzaluna: MATK +15%
The best attack combo would be Weapon(Gerust), Armor(Moldus), Additional(Tarna), Special(Mezzaluna) which gives 20%+14%+15%+15% a total of +64% only from Xtals
Xtals like FG, Dunkelis are pure MATK xtals that you can consider for any equipment slot.
However in my opinion a HiWiz can afford the MP recovery negatives if you can place all Dunkelis then you get 4 x 13 = 52%.