1. ichimaru gin/ urahara kisuke (the best imho; both reasonably very powerful -i am not a fan of aizen's fixation with perfection and power and neither with ichigo's bottomless pit of reiatsu- and very... how should i say this... creative warriors, i really like their flexible battling styles and wish we could see them in more fights)

2. coyote stark/ ulquiorra cifer (really unique characters for this manga)

3. sousuke aizen (ok, i know i said that i do NOT like his fixation with power and perfection and it's true: i do not like those aspects of his character which were his two most obvious weaknesses; but there are other things i do enjoy and like: his ability is hax and he could be deadly while using it. he was one of the two -maybe four- smartest individuals of the manga and very accomplished in many ways. pity he was such a douche as a person... shame-shame-shame)