I'm not one thats ever been particular into monster girls as a fetish tbh. Dont get me wrong i have no problem with them and if they are in any adult content ill like it ..but i've never really thought about it in detail.
I suppose i'd say the usual cat girls, dog girls, dragon girls, fairy, angel, fox etc ..or any other type that comes across as cutie style or even loli ..have been done to death imo and i find rather 'basic' ,dont get me wrong smols are in my top 5 genres, but i'd have to give a lead to the more exotic varieties like:
Lamia & Demonic, basically anything less 'cute' and more along the lines of horns, tail, tall, muscular. mommy dom vibes, Futa, this could include more 'rough' styles of Succubus.
I like monstergirls with a physic of a non-human like a centaur or mermaid but the elf or neko girls are just human in cosplay. Only on my opinion of course.
Not a big part of my portfolio, but any of them that comes with a body/part top exploit to make them putty in your hands - sensitive tails to yank, fluffy parts that get overstimulated when pet, petites overwhelmed by your size, etc.
I'm generally more for the softer-side when it comes to textures