Sub-optimal IV's you like more

anyone with workable spd with +spd, even when they have other powerful stat that can be increased more.

I was wanting a +Res -Hp Catria, but they they came out with Fort Def/Res so a +Atk with a Res Refine weapon fit better, though if Catria gets a prf weapon I may still want the +Res IV (only +8 right now).

+Spd -HP Genny. Generally you want to take -Spd and and not -HP, since she is so very, very slow already and you want to keep her magical defenses intact. However, I decided to super invest in mine and now she hits 40 speed before buffs, and running her with my proper setup means she can double nearly everyone; even speedy swords like Ayra and Soleil.

Also, another IV set that I really like is W!Robin with +Res -HP. I run Berkut's Lance++Spd and turned him into a pretty fantastic mixed tank (since I'm running him in an armor team he gets full wards) and is a lot of fun to use.

I tend to love those slow units that they recommend to dump speed on but at the same time have speed superboons. For example, I've been waiting forever to find a +spd, not -atk Bartre and make him as fast as possible.

Also I love to invest in defenses in those units that are already fast enough to avoid doubles and usually perform them. My Shigure is +Def, and I feel he doesn't need more speed cause he also has Atk/Spd Link and Spd/Def Bond which puts him at 48(50 with ally support).

I also tend to consider -Def better than -Res in units that use DC that are not called Sigurd or Seliph, since their defense is usually still good enough and I value magical bulk nearly as much if they're going to face many mages/dragons.

I have a +HP-ATK Ninian that is pretty good for running infantry pulse and nothing more

+Res -Def S!Sharena is a fun ployer/mage tank

I decided to stick with my +Def / -Spd Azama instead of looking for a -Atk one because 1) getting doubled helps charge his special faster, and he's so dense that physical attacks often do no damage anyway, and 2) even though his attack is tiny, if he's the last one left on the field with a unit he can barely hurt but who can't hurt him, not having an attack bane sometimes means the difference between him being able to eventually finish the fight and me having to surrender.

Also, I decided I prefer a +Atk PA!Shigure to a +Spd one. I've got Inigo if I need +Spd, and Shigure's attack is really pretty strong. I try to invest in both of them, though. As a support unit, he tries not to get attacked at all, and when he needs to do some attacking, having strong attack and secondary speed helps him do what he needs to when it's called for.