How Secure is gpg Command Using Symmetric AES-256 From Being Cracked How secure is any data encrypted using the following command:

gpg -o *encrypted_output_file_name* --symmetric --cipher-algo AES256 *file_to_be_encrypted*


Can anyone depend on this to encrypt and archive personal content in a public store? 

Please provide details as to which attacks it is vulnerable to, and describe better encryption alternatives if any exist.
GPG's AES-256 symmetric encryption is believed to be as secure as it is difficult to


guess the passphrase
or compromise the machine used to perform encryption and decryption.


Guessing the passphrase should be harder if one uses

gpg --s2k-mode 3 --s2k-count 65011712 --s2k-digest-algo SHA512 --s2k-cipher-algo AES256


or equivalently puts in the gpg.conf file:

s2k-mode 3
s2k-count 65011712
s2k-digest-algo SHA512
s2k-cipher-algo AES256


These options increase (to about the maximum possible per the OpenPGP format) the amount of processing to transform a passphrase into a key, hence the resistance to brute-force passphrase search. This is not a substitute to using a hard-to-guess passphrase, but does help significantly.

When encrypting to self, it still makes a lot of sense to use asymmetric encryption: that allows to encrypt without a passphrase, limiting its possible leak to decryption. I use this for automated backups in the cloud (with a different asymmetric key to sign the backups). I can confidently say that nothing on the machines doing the backups allows to decipher the backups.