Your choice should be based on - memory available ,speed,Device etc ...
Generally for Embedded Systems look table based implementations are preferred ..
I personally prefer AES ...
here is one example AES ...
h**p://edipermadi.wordpress.com/2008/01/21/implementing-aes-using-pic16f84/
Hash Functions are another option.. You can generate Hash value of the password and store it When a user enters a password on such a system, the hash value will be calculated and if the hash value generated from the user's entry matches the hash stored , the user is permitted access.
here is a list of some hash functions
h**p://www.larc.usp.br/~pbarreto/hflounge.html