Endgame incoming? I hope the author actually continues the story, developing the relationship between MC and the chosen girl, not just timeskip to the wedding. Some slice of life with their new life as a couple, you know? It's incredibly rare on harem manga and it's a shame IMO.
My guess:
1) Itsuki: She is the girl that showed the least interest on Fuutarou and also the least developed girl in the series IMO, right now she is almost exactly as she was on the beginning. I'be very disappointed if she was the one picked.
2) Miku: I personally think she is the one with the best sinergy with Fuutarou, when they are together they seem to click really well. Her lack of proactiveness is a big problem, but she grew up a lot during the series and made her feelings clear to MC, so I think her chances are good. I'd be happy with such an ending.
3) Yotsuba: well... her development was huge but also really, really abrupt. Her arc was the most powerful in the series IMO and certainly left a mark on all of us, but I doubt if Fuutarou is aware of how strongly she feels about him. I have no doubt they would be very happy together and would be very pleased if he chose her, but I think it's unlikely.
4) Ichika: I think that her ship sunk and exploded really really hard during the "snake Ichika" arc, Fuutarou forgave her but I don't think he will ever come to like her like that, just remain friends might be for the best. The most unlikely choide IMO, and I would be very frustrated if he picked her.
5) Nino: she is a really, really strong character. Very developed, has very strong feelings about him, is the most proactive and is very family oriented, so I think she would be one of the best picks, no doubt. Has a very good chance and I would be very pleased if she was the one wearing that bride dress.
6) Harem route: I WANT TO BELIEVE. Really, really unlikely... but I think the author could make all arcs actually, make the next chapter a "branching point", and do each girl's arc in sequence, "resetting" after each one. That would make me the happiest, no doubt.
So my rankings are : Miku=Nino=Yotsuba>>>>Itsuki>>>>>>Ichika. Let's see what happens.