You're staying at the Contemporary in June and you're looking for breakfast suggestions in a monorail restaurant?
THIS June? Starting next week June?
Do you actually have a lot of options for breakfast reservations? I haven't checked but this soon out you might not have many choices in the first place...
Of the three you listed I prefer 1900 Park Fare most. Plus some of the characters aren't completely covered in masks so the interactions aren't all pantomime, plus I think the food is the best of the 3.
Chef Mickey's, the food has gotten really mediocre, but at least there are a lot of options.
'Ohana, the food is mediocre AND limited - some island themed breads, scrambled eggs, potatoes, sausage, bacon, mini Mickey waffles...I think that's about it.
Food at The Wave is very good AND it's rarely busy there, so right now it's probably your best bet to score a reservation. You can order off the menu OR do a pay one price buffet, which is convenient if one of you is hungrier than the other.
Kona Cafe is also very good and also usually-not-very-busy so you might have a decent shot of a reservation there.
Grand Floridian Cafe is meh.