I love the vast majority of Louisa-related names, including Louisa itself, but I think there's something special about Luisa. It's more elegant than Louisa (not that I think Louisa isn't elegant), smoother than Luiza (not that I don't think Luiza isn't smooth) and more interesting than Louise (not that I think Louise isn't interesting, though it's certainly overused as a middle name and underrated as first). Luisa is sophisticated, classic, feels slightly vintage though I have no idea how it's received in its countries of origin, yet youthful at the same time and I think it ages extremely well and fits a woman any age and could potentially fit many different personalities fairly well. It's really beautiful and incredibly feminine without being frilly.
A noble woman elegantly steps into the room. She has a perfect complexion of dusky, dusted tan and a full head of flowing, thick raven-black hair. Her gaze is strong, her chin held high, a trace of defiance. She is beautiful. Either rich or poor, she does not boast or beg. Pride. Even in the most awkward moments she is graceful. Intelligent. Firm but fair. All in all, she is a presence. This is what I see when I hear the name Luisa. Love this spelling, by the way.