Stanford and Cal are now in the ACC. Clemson and FSU are not AAU institutions. So my preference, if the Big Ten must expand further, would be for UNC and UVa. Both are similar universities to Rutgers and we already have some history in a number of sports with both of them. Together, they would be contiguous with all but the new west coast members and they are reachable by more fans for away games.
But I strongly prefer that all of this stops at 20 member institutions in any individual conference. I hoped it would stop at 16, since anything beyond that means that the schools and their fan bases won't even really identify with one another. And now living in Tucson, I've witnessed what has happened out here with the demise of the Pac12. An entire region of the country now lacks a top level university sports conference. I feel bad for the fans of Wazzou and Oregon State. I know how worried RU fans were about being left out back in 2011 and 2012 before the B1G "saved" us.