Guise is more effective. I zero gemmed 4, 5, 6 and six with the same team using Darv lead with any random BB spam friend. Darv, Zel, Melchio(Lexida/Sol for BC generation), Elza, and Lillith. The fights aren't difficult if you have the units to make a similar team you just have to play around the mechanics rather than faceroll it down with crits.
Was kind of disappointed in FH8. Cleared every reward on every level first run by wide margins and with only nine runs I was still ranked in the 3,000s last I looked. Need a level past terminus that's neigh impossible to bang my head against : /. Something along the lines of 6/6 for the first stage but with double the HP.
Oh and for Trial 4 2/3 you need to take Emilia and May through 75 and 50% at the same time. Couldn't find legit info on that one and had some trouble so thought I would mention it. Might need to do the same for 25% as well but I took them both down from like 40 on the same turn. You can take May under the % a turn before Emilia if you need to or fuck up. Her shield lasts 2 or 3 turns I forget. Even with it make sure to mitigate though bitch hits for about 18k at 50%. May can be cursed as well so when you use a SBB to kick them under a threshold don't use Elza haha.