As far as the strength of AES vs. 3DES, the difference is probably negligible for most practical purposes. AES is however the newer standard, and is more flexible, performs better on different hardware etc, so seems like an overall better choice, but I would say not so much for any practical security properties. (i.e. both are pretty strong).
You can get a list of the available cipher commands with
openssl list-cipher-commands
A description is available if you do
man enc
Doesn't seem to be any reason you couldn't use AES-256-CBC if you wanted to. Not a security expert though, so other than speed concerns, I don't know the repercussions of doing so.
