Danzo is ok,but you really should get edo Nagato,4 stars(I know,it will take months).He is maybe the strongest ninja you can get from collection.And with his skills-immunity suppress,chaos,increase chakra your opponent need to cast mystery,increasing opponent mystery CD,immunity to interruption,and debuff reflect,it's a solid ninja to have in your team.He also get support from both Akatsuki,and edo tensei.

Other you can get are Asuma(Wind blade) and Shikamaru (Chunin),pain Gakido and Jigokudo