GPG is very secure, as long as your passphrase is long and strong enough. In practice, your passphrase will almost always be the weakest link.
I recommend using the following command-line flags:
gpg -c --force-mdc --s2k-mode 3 --s2k-count 65011712 personal.zip
This instructs GPG to use a password hashing method that is as slow as possible, to try to provide a bit of extra resistance against password guessing attacks. It is not a replacement for a good password, but every little bit helps. You can put the
--force-mdc --s2k-mode 3 --s2k-count 65011712 in your
~/.gnupg/gpg.conf configuration file, so you don't have to type it every time.
Note that GPG does not conceal the filename, so make sure the filename is not sensitive. (I think this is pretty obvious.)