Personally I would like to hear the truth from Hiruzen and Hashirama

Hiruzen because he lived the longest and probably has the most knowledge of Konoha's history. He also was involved with the Uchiha Massacre so his explanation will probably have the biggest impact on Sasuke's final decision.

Hashirama because he fought against Madara and can really put the past in perspective (like the war with the Uchiha, their allaince, and the foundation of Konoha)

Tobirama - He will probably just talk about creating the Police force and whether putting the Uchiha in charge was a sign of trust or just to keep on a leash.

Minato - no offense Minato fans but I really don't what he can reveal besides the fact that the Masked Man (now none as Obito) was really the cause of the Nine-tailed attack on Konoha, he died much too young in my opinion and everything he knows Hirzuen should know as well. But I am excited to see his reaction to Tobi being Obito.

So my vote goes to Hirzuen.