People always say Mei but honestly people are kinda thinking of the fact other series have characters like like Izuku and Mei work or other characters who don't seem like they match at first but actually work together, and also have a fun dynamic. Hatsume has a interesting dynamic with Izuku but it's not really a great or the best one from a romance angle or even as friends, sure Hori wrote her with moments of making Ochaco jealous and touching Izuku and being who fixes and upgrades his hero costume, but her personality and how she is doesn't match with Izuku completely and only works if she goes through specific character growth, plus you'd have to write Izuku getting his costume damaged a lot or Mei out of the support item room.

With Mina you would need a lot to rewrite as well and change but it wouldn't be much or too drastic and already their dynamic is something pretty fun being as Mina is the teasing type who'd probably tease Izuku a lot and make him flustered but she also has a enthusiastic and fun attitude that can work with deku's early enthusiasm he often showed with Ochaco, she definitely would support him  which is a lot more important for a partner or friend for Deku than people think, you can even weave Mina's trauma with Gigantomachia into their relationship or be on its own still ( nothing wrong with a character getting help with overcome their personal struggles. )

Idk if it's a hot take to say that Mina would be best choice for someone else Deku could logically be with if he wasn't gonna be with Ochaco or Ochaco wasn't around. ( Not saying you can't like your own ships or head canons,I even think Izunejire would be a good one as well if written right.)