I am going to go with Katy. I think she will struggle a few more years before she wins a Grammy, but Aniston is never doing it imo Maybe a nom at some point and even that is unlikely..
Aniston is a great actress, but she excels more in the romantic-comedy genre, which is usually neglected by the Academy unless the movie is great. Katy on the other hand, she's already an icon and she constantly gets nominated for Grammy's. Eventually she'll win one.