Which La lillina is the best IV's

Its tough. Personally +def -res seems the best option to me. Her bulk will be balanced and can make for different builds down the line. Like gronraven and brash assault desp. And her speed can be salvaged if u want.

+res -hp is also good for ploys and staying under 40 hp for easier ardent sacrifices for set up.

+atk -spd is best overall tho for you though it seems. If you dont care about arena score (only 1 less point). Its better for ohkos with gronblade.

Atk ploy is just WAY too good but only if u run mixed teams. If you dont plan that then merge

I would suggest only going merging 3 total and holding the last one for skill inheritance as atk tactic 3 only comes on her and seigbert(unless you really need that 1 extra hp and res). As for which one here’s a brea down for you depending on how you want her to perform offensively at merged to +2

(+def-res) & (+res-hp)
Base atk/Spd =36/31
-needs some work to hit two shot blade tome builds, but can still be done with the proper a skill, SS seal and ally support add chill speed 3 to someone on your team as well as debufging a fast target by 7 speed can help out a bunch
Ex)L&D3 w/S+3 seal =41/39
(39/37if you opt to use fury 3 instead)

With blade tome and proper buffing her firing atk can reach 84+ with L&D3 or 82+ with fury 3

+def-res don’t really help her much and hurts her arena total scoring potential as -res is a super bane
-hp+res has means worse overall defensive bulk, but can potentially run ploy skills if you go with fury in the A slot

(+hp-atk)
-Don’t build her

(+atk-Spd)
Base atk/Spd=39/27
-more optimal for oneshot builds and such, as even with heavy speed investment she will only hit 41 or so speed making it somewhat harder to double foes reliably. Death blow3 atk+3 sacred seal means a basic atk of 48 can be achieved on player phase before accounting for blade tome shenanigans that could stack another 43 or so onto that number bringing her to an effective 91+ atk unit

Hope this helps you in coming to a decision!