Linde or Ishtar?

Linde based on ivs. Shes a better support too so that's another reason

Both have pretty bad IVs, Ishtar getting the butt of the fish seeing as she needs speed for improved offenses, and for Linde, HP improves her bulk while the -defense hurts it, but she seems the better of the two.

Honestly depends. Ishtar can reach 52 attack and 43 speed on initiation just with Mjölnir and Swift Sparrow alone, and she has a Special accelerator, meanwhile, Linde has her Aura refinement, which gives her 5 attack and speed, and her Aura tome gives her a supportive role.

Linde is probably the more 'flexible' of the two, and she can reach speeds greater than a speed-bane Ishtar IF she has skills like Life and Death, Swift Sparrow, etc, AND she has her Aura self-buff effect active.

I'd say Ishtar. Though the people here have stated that Linde can reach faster speeds, it requires you to run Life and Death (already lowering your def further), Swift Sparrow (rare as all hell), and it then adds unto the situation by saying that you need to run the Aura refine, and as such requires you to use a very expensive and rare material (divine dew) and as such, I recommend Ishtar. She's more consistent with her offenses, and doesn't require you to put a specific unit in your team to maximize her potential as a unit, while Ishtar can work well with her Bane and with buffs she can overcome them.

In short, Ishtar. She's consistent, doesn't require the refine to reach the speeds she has at the moment, and has a incredible base kit. Linde can work if you truly adore her character and are willing to waste the divine dew to boost her up. And to boot, though -spd may not be best, your Ishtar can potentially take a hit from a DC sword unit and live, allowing her to enter Desp range more often than not.

Well I really love Linde and she was my most used blue caster. I got Ishtar around the time Linde got her refinement. I feel like Ishtar is a bit stronger. Any pulse skill and her tome let her drop 2-turns cd from the first attack and then every fight.
I also find it harder to build a team to really use Linde's new tome. Especially with BST restrictions a mages or a mage and a healer make it hard to run those teams in any rating based mode. Had a Mage emblem for a short time which was fun though xD Linde, B!Tharja and Rhajat with Noire for Infantry push.

I came across a similar issue today. I had dismissed a +HP/-Def Ishtar I pulled awhile ago for future foddering because of the bad IV and I already had a +Spd/-Res Linde I was gonna build. Well, I looked at the Ishtar again today and decided to put her in the calcs against my Linde. Well, I was definitely a little shocked. Linde at her most optimal is basically equal to an essentially neutral Ishtar with her base kit. It's ridiculous. Ishtar even covers the same team support role with Odd Atk Wave that Linde gets from her refine, without the specific ally requirement.