Better spend?

Hmm wow, both are good options for your team.

Mae has a good boon but bad bane, however she gives the team a little more utility since you already have an Azura who can take care of reds regardless of her IV. The magic damage should help more.

Roderick on the otherhand has a great IV set for utilising his lance. With LnD or Swift Sparrow, he can become a offensive God. You can decide to save his lance for someone like Cordelia who runs the best Firesweep Lance set out of everyone, but Roderick is also a great choice and obviously comes with the weapon by default.
Roderick also helps against strong Vantage!Distant Counter reds by bypassing Vantage, and he and peri are good Firesweep Lance users on Horse Emblem if you ever decide to run one.
He just needs Hone Speed to become more affective.

I was originally going to say Mae, but I'm going to advise Roderick now (do keep in mind though that Roderick is also a great skill fodder).

I have a couple of question. Are you a F2P player? Do you like any of these characters? If you don't like any of them and are a free to play player, keep you feathers.

While Roderick has a decent nice, he is not that awesome either, but he does fit your team decently. As for Mae, with a +atk boon and spd, I would suggest you go for a Sanaki like raven build, except her color fit the archtype perfectly I think. It will cost you a male 5 star Robin though... So if you like Mae, she might be the best long term hero of the two. Roderick will be the best right of the bat as Mae will have a hard time using her desperation skill with only 28 base speed.