Comparing these two as units might not seem important since they're not the same, but they fulfill the same role as a red sword. Things like Marth's falchion having no cooldown reduction can be easily fixed by a heavy blade seal and him getting buffs (i.e. his fire emblem which would put him at a nice 58 attack) at the cost of a seal slot of course. Marth relies a lot on his "buffs" though, and isn't as purely reliable as Ayra, but if used in the right hands, he can easily overpower her. Marth's special also buff's the entire team, which might be important. Ayra is also waifu material, which adds a lot.
I think the final choice, while not being clear as day, is most likely Marth as the better, unit, and dare I say, better Ayra.
(Reddit likes him so he's shit though)
