We assume Sasuke's EMS has Madara's powers n he has Itachi's Susano'o while Nagato has all his six parts includin himself all fightin at d same time. I say Nagato cos Sasuke is gonna get tired afta fightin all of dem at d same time.
The truth is we cannot make any assumptions on who is gonna win.
Recently we saw Nagato experiencing a transformation... so we haven't seen the complete Nagato.
For Sasuke... we haven't seen him in action since his "upgrade".