I've played this game a lot now and on my 3rd post game, this is the setup I like the best. At level 255 this setup should max ATK, INT, DEF for most characters while adding some very useful factors and not stacking useless factors like Atk + 18% when you have 9999 ATK anyway.
Imperial Armor (synthed with tri emblems) --Recover 3% MP periodically (provides infinite MP basically) --Nullify HP damage 25% of the time --HP + 20% --Defense +20%
Armor for Meracle/Reimi:
Absolute Protector (synthed with tri emblems) --Nullify HP damage 25% of the time --HP + 20% --Defense +20% --Defense +20%
Armor for the mages:
Laser Armor (synthed with tri emblems) --Nullify HP damage 25% of the time --HP + 20% --Defense +20% --Defense +20%
Accessory for all except mages:
Anti-void amulet (synthed with tri emblems) --Immunity to void --Immunity to stun --Immunity to silence --Rush Gauge charge rate +3
Accessory for attacking mages (Lymle, Myuria):
Anti-void amulet (synthed with tri emblems) --Immunity to void --Immunity to silence --Def + 12% --Rush Gauge charge rate + 3 OR INT +10%
Accessory for healing mages (usually Sarah):
Anti-void amulet (synthed with tri emblems) --Immunity to void --Immunity to silence --Def + 12% --Increase chance of surviving incap via fury
Wrist for all:
Tri-emblum (synthed with tri-emblems and 20 resistance to all elements) --Hit + 2 --Def + 12% --Rush Gauge charge rate +3 --Immunity to paralysis
For Edge and Arumat,
their defense will hit 9999 with only one or two of the ATK/INT/DEF/HIT/GRD + 5% factors on their weapons. You may replace these with factors like increase critical hit chance, etc. as you please. These guys also easily hit 9999 ATK and 9999 INT. I love the periodically recover MP factor because these guys will never run out of MP. They recover around 100 MP every 5 seconds or so and I can't use their MP that fast.
For Meracle and Reimi,
their defense will just hit 9900ish and their ATK easily is 9999 as well as very high INT which is useless anyway. You could upgrade their weapons with tri-emblums instead of infinity sabers in order to get extra HIT and sacrifice the INT, but their HIT will be around 3500 anyway without it and Infinity Sabers are easy to dupe (1 clay each).
For the mages,
their defense should break 9000 which will have to do. It is very hard to get their defense to 9999 without sacrificing some important factors. All other stats are very high, but to hit 9999 INT, especially for Lymle, I synthed a few Onyx Sabers (11 clay to dupe, so farm some clay).
Onyx Sabers appear to be the best synth for weapons in the game. They add 205 attack and 241 INT each whereas tri emblems add 150 ATK, 100 INT, 100 HIT.
I'm looking to max INT more easily for characters like Lymle who used all her weapon factors to boost her fire spells. Is there anything better than Onyx Sabers for intelligence? So far, I haven't found anything better.