My bet is BYU and Cinci. I definitely don't want Houston, don't need another Texas team, and Memphis just isn't on the same level. They may be one of these days but overall just aren't there yet. Now if they want to go to a Big14 then I'm fine with adding all those schools. Actually I'd rather add Boise State and leave Houston out.
FYI, Memphis beat BYU 2 years ago in the bowl. And Memphis is way better than KU in football and could add a good basketball program to the mix.
Memphis would also put the BIG12 smack in the middle of SEC country. Other than the Grizzlies, there are no other competing sports teams in the area.
Big12 already has the city of Houston so not sure why they would add them. Texas teams would't be able to go into Houston and away recruits with playing in the Big12.