Right now, there is little evidence to support any one choice. However, we know all five have feelings for him. They all held his hand at he snow festival, indicating they all will be destined to be with him in some shape or form. There are multiple wedding dresses so we know it's not just a one-off thing. Additionally, the Quintuplets often refer to being "five parts of a whole," and that they cover each other's faults and make themselves stronger, which indicates they will always be at each other's side. Things like who kissed Fuu at the bell, when it is known they can disguise themselves as each other indiscriminately and do so at will, are either red herring or strengthens the analogy that they're all one "functional unit" as it were. This is why he says that he's not going to choose anyONE of them, because he does love them all to an extent. The harem ending here would probably be the most solid in that sense. Granted, he will most likely marry ONE but will still cohabitate and love and care for the rest, living together, working with one another, etc. Hence the title, the five-part bride or the five-wedded brides, Indicating they will all have some role in the marriage.