Both of them are great characters, but Kaori would have been the better pick if she lived. I mean, the personalities between the Kousei and her may be opposing, but their chemistry overtime complemented each other perfectly. Let's also not forget about the letter, because she was inspired to by Kousei to play the violin and did have a crush on him for as long as she can remember. Tsubaki is also a good pick because she has been friends with Kousei for a long time. Plus, her goal to go a high school that was close to his showed that she did not want to leave him.
Both of them do have their problems. Tsubaki did have reoccurring problems that I noticed throughout the anime. As she kept on denying Kousei is the one and never gave him a chance, despite her best friend and the environment itself pointing at him. She did tell Kousei that she will be his guardian angel at the end, but I did not think that it indicated a romantic interest. There was only one problem with Kaori I noticed, but it was a significant one. When going back to the letter, it was very heartbreaking to know that her feelings for Watari were nothing but a fluke throughout the series, giving Kousei no chance to try to confess before she passed away. Both of them also share the problem of treating Kousei like crap from time to time.
In the end, both girls have their reasons for their romantic relationships with Kousei to be canon, but Kaori in my opinion is the most logical and realizable choice. |