Is my high school cryptography/steganography science fair project practical?
which cryptographic algorithm and which steganography technique put together will result in the most efficient, secure data?


AES and DES are already a combination of separate algorithms involving multiple steps each.  They are already "put together".

Steganography won't add additional security because of Kerckhoffs’ principles.


  In what way other than encryption time should I measure the 'effectiveness' of the two techniques?


Computation time is not a good indicator of security. If AES and DES are used together, the security will be equal to AES' security by itself.  This is because DES' seed can be guessed faster than brute force - it has been broken.


  Is this a practical project? Can this be executed like a true science fair project


It is not a practical project because neither AES nor DES can be broken using any machine you own, therefore output (no matter how much you massage or analyse it) will always appear as random bits.  This means there will be no way to measure the security provided by combining methods.