I prefer all white. Other solid colors are less desirable. All white shells with very lightweight patters on the tape panel are okay too. (carousel, vintage, teddy) I also like FUN patterns (little paws are great though the picnic tablecloth sides could use a redo, somewhat less with tykables)
I think in the end I am looking for diapers that strongly reinforce "you're really wearing a diaper!" in my head. For me, what I've remembered from the past is the big thing - and that was all white plastic, but toward the end there was usually a lightweight pattern on the tape panel, and I think that's why I like that too.
For me, heavy patterns (little squirts, idyl, princess, etc) are just too different looking than what I'm used to. Little Paws get a Pass from me because of how well they pulled off babyfur.