73

Sheldon Cooper feels that 73 is the best number:

"73 is the 21st prime number. Its mirror 37 is the 12th prime number and its mirror 21 is the product of multiplying (hang on to your hats) 7 and 3"
"In binary 73 is a palindrome 1001001 which backwards is 1001001 exactly the same."

OK, 73 is a palindrome in binary (1001001) and 37 isn't (100101).

but they are both palindromes in morse code:  
37 is     . . .  - -    - -  . . .      while 73 is  - - . . .    . . . - -