I don’t have one. I’m of the very gatekeep-y but sincerely-held belief that it is bad and lazy GMing to rely on generic fantasy clichés. I make custom monsters or use unusual and more interesting variations like the Mork Borg goblin who curses others to turn into goblins by simply attacking them. Even then I describe them as differently than typical because why be boring when you can do something interesting. I also tend to heavily prefer NSR, Art-Punk and imaginitive anti-canon settings like Electric Bastionland, Vaults of Vaarn and Ultraviolet Grasslands.
I like to use about 65% fairly well known and iconic monsters (if often tweaked!) and for the rest monsters that I am sure my players have never heard off.
I honestly think the bestiaries of Shadowdark & Index Card RPG are extremely good. What they both have in common is that they have a pretty broad range but each monster has just enough stats and description to be very fast, fun and easy to run in any system & ICRPG also has some tweaked or more unusual monsters. I used to hate having to read a full page of tiny font text + a massive statblock for 5E monsters. In many cases, by the time I got done reading I had already forgotten the metric buttload of attacks, immunities, defences and numbers each monster had. So any bestiary that gets away from all of that = good!
Half the time I don’t even use any bestiary anymore. I simply make it up as I go along (especially since I have read so many Monster Manuals, I have a decent idea of what is both “fair” and internally logical and consistent with the system and world I am running. Two things have really helped to make this possible.
a. I have told my players to not expect even every Orc to have a very similar AC or HP total, just like adventurers level up, have different stats, find equipment so too can monsters (within reason) and especially if it concerns mythical or magical creatures,… For instance there is no reason why a huge barrel Mimic should have many stats the same as a tiny coin chest Mimic.
b. My players trust me and that I won’t do unfair or illogical stuff because I roll everything open, I usually tell them after first successful hit what the AC is, and what the bonus for the creature(s) attack(s) is and finally on the back of a paper I always write the creatures HP total and stick to it, and show them after the battle! No fudging. Also, I tell them whenever an opponent is bloodied/has lost ca. half their HP.
I know this is a bit Meta/not best answer to original question but I find the more you do those things above the less you need a minimum much less a large bestiary. I have also found that spending the time I used to spend finding, reading and trying to memorize even (succinct) monster stat blocks and descriptions is far better spent finding 1 or 2 pics of each monster to show my players on the monitor. It adds dread, immersion and on occasion even informs them of what attacks to expect and tactics to use.
Thursday I used two 80cm giant centipedes, I had Zero idea what the stats of those would be, don’t recall from any RPG reading i’ve done. Nobody questioned my DMing of them, in fact I kinda went against expectation when the mage wanted to see if they had some sort of venom to harvest, they didn’t. Internet said: “Many centipedes are venomous, though not all are.” Mine were a strange, giant, probably magically created form of Centipedes, so, I can do what I want. xd
I’ve been trying to come up with more of my own. DCC has a good spiel on unique monsters. Even little alterations make things more novel for me, like calling goblins Figlings and having them barf tar or something silly.
Cool. Quite often i’ve found odd versions of monsters or completely original, sometimes made up on the spot ones, can become a real inside fun moment or kind off be a world-building thing that players end up enjoying immensely and referencing years later. Their first Figling your players will remember, another / 32nd standard Goblin they cut down with ease and that is just like previous 31 they encountered at other sessions, very likely not.