Elise or Lucius?

Elise all the way. Best offenses, and on a horse.

Elise all the way. Best offenses, and on a horse.

That Genny has perfect IVs. I don't know which IVs has your other Genny, so I can't advise you.
And about Lucius or Elise, I prefer an offensive Elise because she can get Cavalry buffs.

Elise by far is better.

Between those two, Elise, but I recommend thinking long term and starting on a Priscilla/Clarine/Nanna merge. Merged healers are amazing in t20 arena alongside higher score units, especially those with strong mixed phases, and are generally a lot of fun to use.

Also, that's a really good Genny so if your current one has meh IVs and you've only given her ATK+3 and Savage Blow or something, it is worth keeping the new one and foddering your current. Losing 50 refine stones sucks and all, but... +atk Genny...

Elise is by far the best healer, with stellar Atk and Spd. Plus, despite the fact she's a cavalry unit, she scores the highest of all the healers due to the fact they're all in the 145 BST bin.

BTW, you can merge the old Genny into the new one, and the new one will still inherit the refine. Nothing is lost when you merge - blessings, skills, and refinements are all kept, no matter which way you merge.