Here's my rubric.
10/10-Highly attractive and functional base that perfectly complements the figure.
Examples: Koto's Gothic Lolita Asuka (mfc link) with the cool stair base, this (mfc link) Koto Asuka, Beagle's Chris (mfc link).
8-9/10-A base that is not only functional but is attractive.
Examples: Koto's recent Sakura Kinomoto (mfc link), GSC's Triela (mfc link).
6-7/10-A base that is functional but possibly plain and boring.
Example: Taito's Pochaco (mfc link).
5/10-A base that is of questionable functionality.
Example: Sega's Sakura Kinomoto (mfc link).
3-4/10-A base that can be made to work, but requires some effort by the owner of the figure to actually be made functional.
Example: Penguin Parade's Kuroko Shirai (mfc link) .
0,1,2/10-A base that is so poorly designed that there's no chance of being able to use (or even modify) it for its intended purpose. I haven't really come across anything like this, but I don't doubt they're out there...