Micaiah, +speed -res or +res -def

Neither are really ideal. +Res allows for Ploying more enemies and can likely save her from many opponents targeting resistance.

Mine is +Res -Def (not merged) and she works extremely well because I double up on distant counter so she’ll be able to have 30 Def and 53 Res against ranged foes. Although if you want to do the +Spd then I suggest slapping a Life or Death on her so her speed can be brought up to 36, and then you can use you SS slot to use a seal that increases your speed further, or Fortress Res so it cancels out the negative affect on Resistance. You’ll end up gaining +2 ATK, +5 Spd, and -5 Def overall from the L&D+Fort. Res combo.

She'd be able to get more out of Res. Against mages, enough Res can make up for a lack of Spd. Otherwise, she's more suited for player phase, particularly as a one-shot wonder, in which case she wouldn't really need the Spd.

Though if you do go the route of +Spd, Desperation is an option to help against Armors.