Definitely 'The Man Without Fear'. This origin story of Daredevil is a classic. It beautifully tells how Matt Murdock became Daredevil after losing his sight. It shows his training, his relationship with his father, and how he developed his super - senses. It's a must - read for any Daredevil fan.
Well, for one, a great Daredevil story often has a strong exploration of his dual identity. Stories like 'Born Again' really dig into how Matt Murdock and Daredevil coexist and how one affects the other. His blindness is also a key factor. When it's used well in the story, like in 'The Man Without Fear', it adds depth to his character as he uses his other senses in unique ways.
In the comic book universe of Daredevil, there's no common occurrence of him sleeping in a sensory deprivation tank. His sleep patterns and locations are usually not related to such specialized setups.