I like many, but my unironic alltime fave is Khezu
When I played MHFU for the first time it blew my mind, he is an embodiment of everything I was looking for in a game, it's world, it's monsters, it's mechanics. He has the skeleton of a Wyvern which at that point of the game you start to realize are the "dominant" or more common kinds of monsters out there, but it has evolved like an actual real life animal whould do in order to adapt to it's enviroment. It lacks coloration and eyes like most cave dweller creatures because neither are of use, it climbs the walls no problem but it's a slow flyer since he really doesn't need to much, swallows it's prey whole with a primitive lamprey like mouth, and has a second one at the tip of his tail to latch onto walls or the cave roofs of the floor to stabilize himself during some attacks, some primitive worms share that structure and not to mention electric eels.
It's just such a well researched amalgamation of weird animals that works so well to make a "monster" that's also an animal, the way Monster Hunter treats their monsters as natural inhabitants of it's world is perfectly implemented on the Khezu and it was exactly what made me fall in love with it, real life animals don't care to look "ugly", they only want to survive and Khezu has so many cool things going on to do so.
He's also super scary, very Resident Evil with his roar especially, very Capcom.