I did Boma breakfast in December 2019 and Topolino's this past February. So I guess I haven't seen Boma in its current form and I haven't done a non-social distanced version of Topolino's, but I'll give my two cents anyways.
Boma's strong point is the variety of food, and buffet style allowing you to get a bit of everything. I find it more leisurely since you can stay as long as you want without feeling rushed.
Topolino's has amazing food but imo you go there to have some character interactions. Not sure about now, but at least in Feb they came by the table every few minutes, and you will see them twice if you stay an hour. We didn't feel rushed at all, but we were a little awkward when they came the second time and we didn't really want to linger for a third visit. You can order multiple things but it's not as much variety as Boma, obviously.
Long story short, I don't think you can go wrong with either one as they are both at the top of my list! I think Boma has the edge in terms of food just due to the variety, but Topolino's has some of the best food at a character meal and the breakfast pricing isn't too ridiculous. That said, Topolino's is so hard to get and I've only been successful once with a dining alert, so maybe your choice will be made for you! I say if you can get Topolino's, go for it. If it's not available, sounds like a sign to do Boma!