For discussion purposes I'm going to list all the reasons why I think Tadano and Manbagi makes a better couple than Tadano and Komi. The first issue stems from Tadano and Manbagi's friendly relationship and Tadano and Komi's lack of one. Note that a friendly relationship is different than being friends. Tadano and Komi are undoubtedly friends, however they don't have a friendly relationship unlike Tadano and Manbagi. This mainly stems from Komi's own communication disorder, which makes it hard for her to hold a conversation with Tadano often resulting in an awkward atmosphere whenever the two interact together. Manbagi is the complete opposite, often holding many friendly conversations with Tadano which creates an enjoyable experience such as when they went around the festival together in chapter 194 or more recently such as when they were talking about the musical they had just seen in chapter 282.
My next point is sort of a continuation of the last point, Tadano and Komi's relationship would be unhealthy. This might sound like nonsense to you, but hear me out. Tadano idolizes Komi. Sure he's better than most of the other people in his class, but he still puts her up on a pedestal. Idolizing someone when you're in a relationship with them is extremely unhealthy and puts a lot of strain on the relationship itself. And on the opposite end of the spectrum we have Komi who is too dependent on Tadano. Just like with Tadano idolizing Komi, Komi being too overly dependent on Tadano would put a strain on their relationship and wouldn't be healthy for them in the long run. Tadano and Manbagi have neither of these problems.
I think lastly I should talk about what Manbagi and Komi stand to gain from Tadano choosing Manbagi. Manbagi has, since her introduction, shown that she has low self-esteem. This only got worse once she learned that Komi also like Tadano, after which she always talked about how it's impossible for Tadano to choose her when he has someone like Komi pining after him. If Tadano did choose Manbagi over Komi I believe that would go a long way towards giving her a much needed confidence boost. Komi herself, however, is the most important factor in all of this. I believe that should Tadano choose Manbagi over her that her frustration at her inability to properly express her feelings to Tadano would give her the final push needed for her to overcome her communication disorder.
These are the main reasons why I prefer Manbagi over Komi. What do you guys think? Also Manbagi is just too damn cute.