For me, Chihiro is first because she liked Keima for who he was, as immersed in games as he had been before the pact with Elsie. She was also an incredible wingwoman for Ayumi despite her own feelings.Chihiro anywhere other than last is inconcievable. Her defining character trait is that she's plain and boring.
Strangely enough, the way things ended with Chihiro is the reason why I can place TWGOK way above other harem manga. It's a bit of a look inside a guy who by all appearances seems very confident in himself, but only because he melds his fantasies with reality. When faced with romance in reality, he ran away. He couldn't believe that a girl could actually like the real and nasty him.
I don't expect TWGOK to end unhappy, but it would have been interesting to think about how the effects of charming so many girls can go badly when they get a better look at him.