I think that this is going to be a matter of personal opinion or preference.  For my bet (and I think for Tagore's), Ratan is the focus of the short story.  While the title might refer to her opposite, I think that she is the focal point.  I think it's hard to not develop feelings of attachment and loyalty for Ratan because she demonstrates these feelings so powerfully.  From the outset, her characterization is one that shows loyalty, care, and commitment.  Ratan represents that quality in people that transcends politics, social affiliation, and the pessimism that runs rampant.  She is an orphan who devotes herself to the Postmaster's care.  She has no ulterior motive.  She takes care of him, appropriates his family as her own, and she finds purpose in the care and support of another person.  It is here where I think that Ratan gains the most amount of support, in my mind.  Her rejection by the Postmaster is something that is destined to happen, a stunningly painful reminder that sometimes the good does not triumph and that honor does not win out.  She is rejected and is left to wander without any philosophical justification to make her feel better, as the Postmaster is able to use.  All she is left with is the "faint hope" that the Postmaster is to return.  I realize that to embrace Ratan is to embrace someone who has been done wrong and someone who is not, on face value, a "winner."  Yet, I think that she endears herself to me because of this, because there are times in life when all people are akin to Ratan, having to live with the rejection of others.  The only comforts are "the snares of delusion" that encompass us as they do Ratan.  I think for this, alone, Ratan is a character towards whom I cannot but help feel loyal.