The question is which candidate will be up to facing
Mikasa Erza, our Fairy Queen, 
next round.
If Boa won, that means
Brandish vs
Emperor Spriggan next round....
But fact of the matter is, while Riza may come across as more down-to-earth and badass, Boa is this beautiful, strong woman who is secretly completely awkward and adorably horrible at talking to a guy, which you wouldn’t expect from someone like her. She also is made to be a waifu. No she isn’t everyone’s waifu but for the specific person she loves, she would do anything for. If we are looking at wife qualities, I have a hard time imagining either girl in the role of happy homemaker but for Boa — she will go to the ends of the earth to do stuff for Luffy. Because it’s not about which is the better character at the end of the day, but which is a better waifu, and which inspires more romance in the audience.
Vote Boa!!!!!