I think my overall favourite is Ramtasm, good spooky ghost creature, but I also love the weird Coaldron a lot! I like most of the monsters evenly enough, I think? The only line I'd say I dislike (outside of gameplay mechanics) is Allseer, which is more due to not liking "ancient aliens" as a motif than anything else.
I don't think I have any real type preference, either- stuff that fits my tastes is spread evenly across multiple types, even ignoring bootlegs meaning I can get stuff like a fire-type iceberg. Though I still love how Plastic, Glass and Glitter just stick out as weird types for a game in general!