I would be happy to see a Bestiary 1 the same size as the core rulebook (500 page plus) with the iconic monsters (the dragons and giants etc.) but also the best monsters for PF. I would love to see popular monsters from later books in the PF. I don't think just because it was in Bestiary 1 or 2 from PF1 means that it has to be in PF2 Bestiary 1 unless the monster really has traction.
Also the whole range of challenge ratings (or whatever they will be called in PF2). Have a book that covers levels 1-20.
What size Bestiary 1 do you want to see and what monsters should be in it?
I am also in the camp of a large bestiary with the best of monsters as well as the iconic ones. One of the big reasons I never jumped to 5e was because it does not have enough monsters to have a varied number of games.
How many pages would you be willing to pay for in the first Bestiary? Because I agree that more monsters is better.