Oh huh! That's a very interesting question!
My favourite style of graphics is easy; low poly psx type stuff. I prefer things from that era that try to look either very stylized or very realistic. But anywhere inbetween is cool anyway.
But I don't know if I'd say that's the prettiest style of graphics? Hmm.
I guess it depends on how you're defining pretty? If we're taking it as just "what is the nicest to look at" then I'd say probably cell shading? Specifically because the sharper contrast you get from the lighting usually makes things pop much better
Thanks for the question! This one definitely made me think, and might have me coming back and changing the answer at some point