Which encryption algorithm is better and why?

If you're talking about symmetric key encryption (the kind where you just use one key for encryption and decryption), then arguably, the best encryption algorithm you can use is the Rijndael algorithm, better known now as AES (advanced encryption standard). It is the encryption standard used by the U.S. government for classified information. It is fast, requires little memory, and the only potential attacks against it are highly theoretical.

Rijndael beat out Twofish and Serpent in the AES standard contest, but those other two algorithms will provide more than enough security as well. In the end, it doesn't really matter, since most successful attacks are made simply by finding out your key through brute force, espionage or extortion, rather than pure data analysis.

Humans are almost always the weakest point when it comes to security, and it doesn't matter what algorithm you use if someone can guess your password.