Eldigan IV???

Eldigan's speed isn't really that necessary unless you're wanting to build a fast Eldigan, and his resistance is practically non-existent unless you're trying to go for an unorthodox mage-tank build.

I'd go with either +HP/-Res or Neutral.

Two options here, +spd -hp and +hp -res.
The +spd combines well with fury. You could even do a Raven and combo the fury with L&D. Bringing him to 56/36 atk/spd this combined with buffs makes him quite a good offence unit. And his def is still 32 after that.
Push in a galeforce or aether with heavy blade seal and you got yourself a fine monster.
Brazen atk/spd is also a fine A slot

The other option is better if you want to go with Brazen atk/def.
It's the one I got and it's pretty nice. Give him quick riposte and he'll counter at full health and then go to town when his health drops. And even after taking a hit, he should have enough health to keep tanking one or two more axe/sword units (if he avoids specials) since his def gets boosted and his health is probably still above 30.
You could run panic ploy seal with this. If you happen to have a fodder, panic in C and close def in seal would be optimal.

I think he is the perfect hero for desperation/brash assault that can be used in arena assault. Buff him with fortify/hone and he gets very good attack and defense. Put him in front of some random red and he will be in BA range from the double fury, since his defense will be high he will not get killed and even if he takes little dmg the fury will take care of dropping it. Next turn you have ignis ready and... BAM, 2 consecutive hits plus ignis. It's fun killing +10 effies with Eldigan :D