WordNet sense 1 (marked by no especial liking or dislike or preference for one thing over another):

indifferent

WordNet sense 2 (characterized by a lack of partiality):

unbiased

WordNet sense 3 (unaffected by strong emotion or prejudice):

dispassionate

WordNet sense 4 (unaffected by self-interest):

disinterested

WordNet sense 5 (showing lack of favoritism):

fair

WordNet sense 6 (free from undue bias or preconceived opinions):

unprejudiced