In my opinion, it would be better for Kaoru Mitoma to leave Brighton to be able to develop his career at an elite club like Manchester City or Barcelona, which is currently on the rise. Indeed, Barcelona wants these players, but it seems that Barcelona still cannot afford to buy new players, seeing as their financial condition is not good at the moment.
The Manchester duo both want this player, but I am more interested if Kaoru Mitoma joins Manchester City to be able to develop his career well there because Manchester City is in good form at the moment compared to Manchester United.
In line with you, I think leaving Brighton is not only to develop a career but also to win trophies. Kaoru Mitoma will be the hottest property in the upcoming transfer market. I think a number of elite EPL clubs will try to sign this Japanese international player after consistently proving his quality with Brighton. For Barcelona, they shouldn't make mistakes that will embarrass them, I mean with the crisis they are currently facing, it's better to just save their loan proposal, because Brighton will label Mitoma for a high price that Barcelona won't be able to pay for in the near future.
Yes, I hope Mitoma can join Man City, even though he has to fight hard to get a place in Pep Guardiola main squad. If he goes to Man United, I feel his talent and quality could decline drastically and he is prone to sharp criticism which will have an impact on his mentality, that is not a wise choice for his career development in my opinion.