I thought Sanae in UFO wasn't bad. Actually, I can't really complain about any of the characters in UFO, except for Marisa and Nue. I love the idea of a goth loli zettai ryouiki meticulous evil character, but Nue's original portrait is like ".... pleh."
That early PCB art, sans the 6th finger, is awesome. (Also, I like how she's looking all innocent and blushing, but she's discreetly flipping the bird.)
Usually artists gradually improve over time, but ZUN's shit is like a sine graph of skill. O_o TH13 is either going to amaze or horrify us.