I think it's Baylor or Mississippi State.
Baylor's duo is the biggest and they work extremely well together. Both are terrific rebounders and are capable hitting shots from the high post. Offensively they're very well synced and can play well together, although both are somewhat streaky performers. Defensively Brown isnt elite but Cox is strong with her shot blocking and length. Really difficult to match up against. Perhaps even more difficult is you have a really smooth 6-3 forward in Smith off the bench along with a very athletic 6-5 post in Egbo.
For Mississippi State, Anriel Howard is playing more of a 3 offensively and is the strongest off the dribble of the 6 players noted. They're definitely the best rebounding duo and the best defensive duo. McCowan has shown shes more foul prone this year and if she is out Mississippi State becomes very vulnerable. McCowan is the weakest of the bunch offensively, and you don't really see McCowan/Howard working together much offensively like you see from Cox/Brown, but both bring strengths to the table and are very difficult to match up against.
Notre Dame's duo is very good but they are not as difficult to match up with since neither has immense size. Both are great players and I wouldn't be surprised at all if they outplay the opposing duos head to head, but in terms of planning to match up with ND, it's less intimidating matching up with ND's posts vs. the other 2 teams. A lot of teams have a shot to score inside and win the glass battle against ND where that isn't the case with Mississippi State or Baylor.
That said, Notre Dame as a team is more difficult to match up with because you have a phenomenal scorer in Arike, a deadly shooter in Mabrey, and a do-all player in Young. All of their starters average 13+ppg and each can go off for 30 on a given night.
Also think Hebard/Sabally could be on here, they're a terrific duo.