I would say

speaking logically it would be flora, because sunlight and warmth are two key needs to grow most plants. which can provide a physical form of attack, and ironical shade from the light. i dont really see how stella would be very powerful at all?

They are tied imo.

Flora is always the first to fall during a battle and her attacks are very weak.

As much as I want to go with Flora on this one I will be picking Stella.

Hands down.

Stella is the strongest character, in my opinion.

Well, I mean, Stella can create fire.

She could burn all of Flora's attacks into nothing but ashes.

Flora is the weakest character in the entire franchise and you're putting her up against the one with with strongest powers.

Absolutely no contest.

well flora is the fairy of all nature and nature is not just plants and trees , nature can be animals and also the four elements ( fire, wind, water and earth) so flora already has Stella's weakness in the bag. its just that flora doesn't get enough character development in the show and rarely uses attacks mostly defense and she holds the enemy back.

Flora.... because eveything is part of nature, so she is kinda the fairy of everything.

Stella is the Strongest fairy...

Stella wins.