Given how hard it is to deliberately find a lion without the use of dogs, I'd want something that had a bit more Oomph than really needed, and that I could shoot really, really accurately.
IMO, the .223 isn't really enough, and the 12-gauge is not quite accurate enough. Of the three, I'd take the .30-30.
And, pretty much the same choice for black bear.
I'd try to set up for shots inside 100 yards, if at all possible. Dunno where you're hunting, but I'd think in terms of putting out some bait and setting up some 50 to 75 yards away, paying careful attention to the wind.
Art