Harpy is probably my favorite so far, divebomb blowjobs really did it for me. I wish there was more oral oriented things but we'll see in the future. Like it would be great if everybody had an orally satisfied scene, especially if it included 69 or facesitting in there.
In fact i don't mind Urka or the Brigand since i love the content with them but i think the Dullahan's blowjob scene is the best also Urka's Prone bone domination is awesome.
I really couldn't pick a fav, they're all too awesome. I'll risk saying I'm having a fuzzy feeling about Goddess of Mount Xiuh, she looks like a mixture of Pinkie Pie from MLP:FIM + Ezor from Netflix Voltron:LD and it always makes me laugh (in a good way).
Spider Woman. I have a weakness for oviposition and "bad endings". Harpy is a close second, simply because she takes you back to her nest. Can't wait for more on Wasp and Mermaid.
It has to be the Warlock for me. Honestly the Wasp shows a lot of promise, we just haven't seen much of her yet. Werewolf girl and the Harpy are the best monsters right now, though.