Tsunade > Kabuto. (notice the period)

Kabuto is around Kakashi level, taking out anbu ninjas, getting his nervs confused an only taking a few mins to get his body back in working condition, all of the above is something Kakashi capable off.

Tsunade IS the weakest senin because she's so out of practice and she's past her prime, but she is definitely stronger then Kabuto now(as of chp 224). She said his senses and strength may exceed even her own in her prime but she never said anything about him being stronger then her and absolutely did not said he could beat her. What about summoning? Special medical jutsu? Why do people insist on Kabuto being the hidden dark horse super-mega-powerful-evil-dude-kind-of-guy? Kabuto may have an interesting relationship with Oro but he just simply CAN NOT be on the level of senin and he certainly CAN NOT be an Akatsuki member, although .... he could press information to Akatsuki.