Well, if you ask me, we CANNOT judge Itachi's faithfulness and Leadership towards konoha if he is made Hokage. Hence, we cannot say who WILL be better Hokage.
Lets judge both by base.........
- Tsunade:- She was a gambler, better a drunken gambler and a solitary rich women who liked to be herself, and didn't gave a **** to the Konoha. He abandoned the village long ago, and was roaming freely Until Jiraya and Naruto came and convinced her to be the Hokage.
Her past Experience:- Being a Sanin, she is a very powerful women, and her healing abilities and brute force is unmatched. She showed NO leadership as a captain as past, but has most basic knowledge about every battle strategy and politics.
-Itachi :- Itachi was the Konoha ANBU captain at the age of 13. No doubt he was most powerful of Uchiha's (after shisui's death) and ANBU. He worked for the village and was very faithful to it, and protected leaf village even after his death.
His past Experience:- As a captain of Konoha ANBU, he is normally most powerful of ANBU, plus, he have huge knowledge of battle and leardership. But he showed NO political knowledge to run a village.
Conclusion:- By both's lifestyle and hype, we CANNOT conclude that any one of them is better Hokage, being the most intelligent, being the most powerful, etc. does not determine the caliber of Hokage they will be.
For instance, elders have a huge knowlegge about politics, but are not made hokage, as well as naruto, who is most powerful of leaf, is not made hokage.