I can't lie. I love a toy that is both functional and attractive or unique in appearance. That doesn't necessarily mean a glittery surface or a rainbow of colours (though the latter would be pretty fun). Something simple but visually appealing like the Njoy Pure Plugs or any number of Tantus' butt plugs are quite nice. Glass plugs, too, are a perfect combination of visual and sensual.
I think it's more an overall quality thing. Something that is (unintentionally) asymmetrical/lumpy and has a seam is both unattractive and a sign of potential poor material/production quality.