New Sword Project

So I'm starting to build up a new sword project. It will either be Infantry Roy or Infantry Eirika. Roy's job will be to kill dragons and certain swords with swordbreaker while Eirika will be supporting with buffs and Infantry rush. Eirika is plus 1 thanks to a pity breaker, and Roy has steady breath Ignis. Both would also use infantry rush to support my Lyon's Aether charge. Which one is a better investment? I am also concerned with arena scoring and willing to sacrifice my LA! Hector for DC on Eirika if necessary