Intelligence
I'd say they are about equal in intelligence... Hanzo may have more combat intelligence, and Danzo probably more kinjutsu knowledge.
Taijutsu
I'd say Hanzo easily (considering it is somewhat needed in Kenjutsu). He managed to outplay Mifune when the latter was in a more youthful and overall probably faster state. Danzo only once showed impressive taijutsu in kicking Karin... but he kicked Karin who is a support type.
Ninjutsu
Danzo had displayed a better overall scale of ninjutsu; however, it is noted that Hanzo is a fire type. Additionally, Hanzo fights via paper bomb traps so that could also be factored into hitting Danzo as they move around the battlefield.
Genjutsu
Danzo's saving grace for this fight rests here in Izanagi; however, it only prevents his death and the eye closes... meaning that every kill shot would bring him closer to death.
Strength
Considering his age, Danzo probably loses here. Additionally, Hanzo was able to cut through Mifune's sword (a skilled Samurai) with a clean cut just by DRAGGIN the chain of his kusanagi (SP?!).
Speed
Hanzo managed to escape the Gedo Mazo's Dragon Soul Snatching Jutsu. He was also said to be unequal in moving in water. Finally, he has a speed option underground with Ibuse.
Danzo's only notable speed feat was again... Kicking Karin.
Stamina
Considering he took out the Sannin and a platoon of Konoha shinobi without a scratch... I'm going with Hanzo. Danzo was revealed to be getting heavily drained by Izanagi.
Hand Seals
Considering Hanzo has never been seen utilizing any significant numbers of them, I'd say Danzo.
For the most part, Hanzo has the advantage in more of the cases. However, obviously stats do not guarantee victory. Considering his great skill in Kenjutsu, Speed, and Strength backed with Ibuse's poison... I'd say for the most part he manages to dodge the Wind Style of Danzo. Experience wise they are about equal, but Danzo does spend more time in the shadows of Root compared to Hanzo who sits in the Large Country's Warzone of Amegakure.
I'd say Hanzo with High difficulty... because Izanagi does make fights far harder and dragged out than they would be otherwise.