St. John's, for several reasons: the Big East badly needing to show strength and competence in this era of power conference separation from everyone else; UConn gets money; not wanting Duke to win a sixth title (big reason); wanting a chance to play St. John's again after getting blown out ten days ago, partly because we missed nearly every shot in the last seven minutes of that game.
Also, if we fall short, I'd rather have a FF with St. John's in it than Duke sneaking in as the only ACC team left on the board and making the ACC look less lame than they deserve to look. Besides, Syracuse and BC are in the ACC, and a lot of their fans want our state university's sports programs to collapse, as they assume that their walled-off private universities' athletics would magically benefit from UConn going bye-bye (which I frankly doubt). Do not forget this.
Besides, St. John's would at least be interesting. They've only been to one FF in the Big East era and that was when "Material Girl" was topping the charts, so it's not like they're gonna long-term eclipse us even if they somehow win the whole thing. They have a shelf life because Pitino will retire in the near future.