It is Irrfan over Aamir for Kiran:Cinejwala:

Actor turned Filmmaker Aamir Khan at the DVD launch event of ‘Dhobi Ghat’, revealed his dream of working with his wife and director, Kiran Rao. Initially, Aamir Khan wanted to cast Kiran opposite him for their last flick together, ‘Dhobi Ghat’, but Kiran declined the role. Aamir revealed that Kiran is more a fantastic actor than he is and he would love to romance Kiran in a film.

Aamir always advises Kiran to start acting in the films but Kiran is never keen on acting.
Aamir was impressed by the way Kiran gave her voice to the ‘Dhobi Ghat’’s central character, ‘Yasmin’. Aamir wanted Kiran to play the role of ‘Yasmin’. However, Kiran admitted that she prefers non-conventional cinemas to mainstream cinema and hence, she would love to be cast opposite Irrfan Khan who is an offbeat movie actor. Well, this piece of news may disappoint hubby, Aamir.