The size of the small ophidia is more of a day/work bag, whereas the disco can be both a day and going out bag.
I think both are classic in different ways because they are both retro call-back styles, so I don’t think either bag will ever really go out of style. The disco is a bit more discreet in terms of logos, if that’s something you are considering.
I have two discos and they are my favorite bags in terms of chic-ness and functionality.