I own the 1st Pathfinder Bestiary, and the 5E MM; but not the 3.5 MM.
I actually own PF Bestiaries 1, 2, 4, & 6; and the Monster Codex. The original AD&D MM. The 5E MM, Volo's Guide, and Tome of Beasts. (And the 4E MM1, MM2, MM3, & Dark Sun Creature Catalog).
I really dig the Monster books, and I think the 1st Pathfinder Bestiary is an excellent Bestiary. I don't read much love for it online, and I assume that is because the 3.5 MM must have been awesome itself?