Firstly, I have to say I don't want the Big 12 to expand at all. If we HAVE to add two teams I've changed my mind several times depending what is going on with other conferences but am currently of the opinion that Northern Illinois and Cincinnati would be best for us. I know some may laugh at UNI, but I think they may be a diamond in the rough for the Big 12.
The ACC,SEC, Pac, BigTen schools are all off limits. BYU and Boise State are too far away. USF/UCF would make for division headaches, not to mention that even though they get you into Florida they are at best #4 and #5 in terms of interest in their home state. FSU/UF/Miami already have too much football history for us to really gain much viewership in Florida which is what the big tv execs want for our tv contracts.
Look at UNI. They could solve some problems for the Big 12. One, they along with Cincinnati would bridge a gap between the founding members of the league and WVU and two they get us into the 3rd largest market in the United States (Chicago) and the 5th highest population state in the nation. They are really only competing with Illinois and Northwestern in their state. These are two schools that don't really have a lot of long term success in football. If you place UNI in a very winnable North Division and rotate the Big XII football championship games between Dallas and Soldier Field, you're going to start winning over a significant portion of the Chicago market. You could also probably host a couple basketball tournaments there as well although I don't know if they'd be as successful. The exposure would be great for our league.
Why go to Florida and compete with two strong leagues, the SEC and ACC when you can go to just outside of Chicago and try and compete for viewers there with only the Big Ten? It would give ISU another close game too and would help for all of our nonrevenue sports in that division to have closer games. We could also mandate that for Cincinnati and UNI to be included that they must expand their stadiums and until they do they play big games like home vs. OU/UT in Paul Brown Stadium and Soldier Field.