As far as the US government is concerned, AES is the preferred symmetric cipher (i.e. uses the same key of encrypton and decryption.) Blowfish is another, earlier symmetric cipher.
RSA is not considered outdated; it's very much in current use. The fact that no one has worked out a way to break it even after several years of a use is why it's still commonly used.
RSA is an asymetric cipher (with a private and public keys) which is used for key exchange, key signing and verification, etc.
Symmetric cipher algorithms are faster than assymetric ones, so if you're sending bulk data to another person you would not use an assymetric cipher to encrypt the data. Instead, you generate a one-time symmetric key (usually with AES) and then use your and the other person's RSA key-pairs to safely transfer this symmetric key. The data is then tranferred using the symetric key.
If you are going to manually provide a password for the saving and loading of the file, then you should use a symmetric key (as there is no one to exchange with.) But note that the ouput of AES (and Blowfish) is binary, so you would have to text-encode the output of the algorithm if you want to save it in a text file (e.g. base-16 encoding, hex encoding, ...)
But I'm not sure going to the trouble of using a full strength key is worth the effort if you're using a hard-coded key in your program, unless you are going to also go to the trouble of make your app hard to debug (non-trivial.) If you just want to make the data file hard for naive users to read (rather than cyber-criminals) then you could use a less involved algorithm, for example:
Tiny Encryption Algorithm
Or even just XOR encryption.
If you do go for AES or RSA, it would prob be best to go with a crypto library.