Smh at Tobirama being first when his feats are mediocre. Naruto's got country wide sensing, Nagato can sense everything his whole village with his rain technique, Karin can pinpoint people's chakra eg Danzo.
Tobirama his powers are natural
Ridiculous how people put shinobi's that are guaranteed sensors out of the list and put shinobi's who either aren't sensors, or there is no absolute proof of them being sensors. I am certain majority do not even know that kisame is a sensor when he is fused with samahada.
Anyway it appears the manga is leaning towards Karin being the best sensor in the series as that is her noticeable ability therefore i am going with her