this "Full Potential" thing is a bit of a dubious method of argument, imo.
if the character isn't manifesting that level of power in any present time line (alternate universe), nor has access to such power in the present then it just - literally - doesn't exist.
Galactus could potentially eat up the whole universe, wiping out all the Stars that Ororo is so fond of. there'd be no environment left whatsoever.
The Silver Surfer has a portion of Galactus' Power Cosmic, so even he would be more powerful - at "Full Potential" - than a "Full Potential" Storm.
The Incredible Hulk has a universe that he can tap into infinitely, so he positively stomps all over Storm and her godhood. her "million stars" are as nothing compared to his universe. so "Full Potential" Hulk, written that way, would be insanely powerful and superior to Storm.
Magneto could have control over strong and weak magnetism - at "Full Potential" - making him a virtual god of the universe.
none of these characters actually demonstrates such power, though they all have some degree of claim to it (all of them have as much, if not more, of a claim to their "full potentials" as Storm does to hers).
anyway, from what I remember of Apocalypse (ripping the X-Men to shreds in a manner that Magneto would have been impressed with), I'm going to say Apocalypse takes this.