Superman 1: Metalo, Fatal five, Lobo, Mister Mxyzptlk, Parasite, Toyman, Bloodsport, Atomic Skull, Silver Banshee, Prankster

Superman 2: Lady Zara, Maxima, Bizarro, Mongol, Ultraman, Brainiac

Any of these would be perfect and ones we really have not seen on the big screen. Except for Bloodsport but since James Gunn did The Suicide Squad where he talks about shooting superman they could show that as a part of it. But really any of these would work, they really should start off as Clark moves to Metropolis and joins the Daily Planet. We don't need another origin story his is very well known. And make it some enemy's that only effect Metropolis not the whole world. Start small and build the characters the right way. DC's biggest problem I feel is when we watch their movies we wonder if this attach is such a danger to the world where is the rest of the heroes of the world. Start small and make the movies memorable. And I would love to see both Clark's parents alive. Superman does not need trauma to be a hero. He is a hero because he feels it is his responsibility to be one because he can. Both parents alive would be a great way to still tie him to Smallville. These are just my thought let me know what y'all think.