I like both but I'd rather pick Rukia. I like that Orihime is a pacifist but she sometimes overdoes it which really annoyes me. Most of the time someone else has to save her. While Rukia is different. She is more serious. She might not be a seated officer but she is quite strong and determined. Moreover Rukia is a very close friend to Ichigo and accompanies him everywhere. What else makes me like her more than Orihime is the fact that she is not afraid to oppose Ichigo which many times leads to funny quarrels between them.