I think at a distance they are both equally dangerous to one another as they both have decent ranged abilities. However, if Korra can get in close then I think she can win with her superior h2h skills. I wonder if Scarlet Witch could use her powers to take away Korra's bending abilities.
Storm takes this. She can drop the temp to exceptionally cold levels. Or she can just create a massive storm with massive lightning, gale-force winds, and monsoon level rains which can then cause massive floods.