My personal favorite brand: Tatami. 2nd: Manto. If you are looking for very creative rash guard designs, I would recommend to check out Meerktsu.
We’ve also listed some of the best rash guard designs on this page: https://mmagearaddict.com/best-rashguards/ and asked people to vote for their favorite one.
If you guys have some other great suggestions for this list, feel free to post here.