My absolute favourites are from "old-school" anime, like Sailor Moon, Evangelion, Akira, Ghost in the Shell, Gundam, Dragon Ball etc., stuff from the 60s - 90s! Especially with the shining, expressive eyes, the huge hair, the exaggerated anatomy - it's a style I really hope to emulate some day. Studio Ghibli is another favourite, simplistic but well proportioned and expressive. And any art by Kamome Shirahama is just... *chefs kiss* to die for!
I'm an extremely "visual" person so art matters to me a lot, and over the years I've become unreasonably finicky and fussy with anime styles (well... most aspects of anime, really). Now, I won't deny credit to any artist - there is no wrong style, I always appreciate the work behind it etc. - but in general, I'm hugely put off by any "generic" style, as well as things that are just too extreme, like One Piece. It's enough to actually put me off from trying them out (a bit narrow-minded, I know, but most of the time it's very easy to predict an anime from its style!). I'm also not keen on "cutesy" styles, like moe or chibi, or anything that lacks a nose haha.
I am drawn to most styles that deviate from the generic, easy-to-animate styles, especially if there is a touch of realism, like fine details and unique, expressive faces, something to really set characters apart. The Netflix Castlevania has that going for it, I think.