That's really a tough one. Shanks is obviously a powerhouse even though he lost his main hand he used to fight. Before he managed to get on par with Mihawk to some extent in terms of swordsmanship. Though now it seems that he is not at that level as he was when he still had his left hand. Even though it seems that his Haki grows stronger and stronger. He seems to be among the best Haki users in the manga, so it might compensate his loss of a hand, but anyways the problem is his opponent who isn't a small fry.
For now this fight might be the most interesting and the closest one in this Tournament.
Kizaru is obviously a damn powerhouse as well. He was shown to be among the strongest Marines. He was shown to have Haki and be quite a professional in it as he was fighting quite comfortably against Rayleigh who seems to be among the best Haki users so far and also among the strongest swordsmen. He has one of the strongest DF's in entire manga. It has an enormous destructive power on par with Enel's DF and has even greater speed than Enel's, thus Kizaru seems to be the fastest guy in the manga for now. I do believe he was stronger than Ao Kiji and maybe on par or even stronger than Akainu. The thing why he didn't become Fleet Admiral, it's because he didn't want to be one. It even seems to be a bother for him to be an Admiral. He was never shown to be serious. Neither during his fight against Rayleigh, nor during his presense in the War. I believe his actual fit that might give him some edge in this fight might be his enormous speed. Especially since Shanks doesn't have a hand and thus it limits his ability to block attacks from different directions. Also we shall not forget that Kizaru seems to be a swordsman as well as he fought Rayleigh with a swords made from light derived from his DF.
Still, it's really difficult for me to decide this fight, so I'll wait for more opinions.