I generally go by how distinctive a character look when it comes to chara design, and as far as Touhou goes, the girls featured in Bad Apple can be recognized despite everything being in black and white.
As for the big name that is suspiciously absent from Bad Apple, Cirno (yeah, she's not in the PV and nobody and ever remarks that), her chara design is a VERY simple blue and white color scheme plus distinctive crystal wings. There are more adult looking or longer haired Cirnos elswhere, but these few traits just allows one to identify her instantaneously. So yeah, pretty cool chara design (no pun intended) as far as the ice fairy goes.
As fot the more modern girls that are not as simple as the old ones, I just like Toutetsu despite her having a lot of stuff. She's goat the most unique head among the cast what's with the curly horns wit bows, the short and very wavy hair, gremlin piercing on the gremlin ears, the sharp oil-eating grin, and the goat-like "-" in her eyes (whatever these are called), which are suspiciously absent in her ZUNart. Also giant spork.