First off, this is a poll. Second off, before you vote consider this. The SEC cross division rivals currently stand at Alabama-Tennessee, Auburn-Georgia, Arkansas-South Carolina, Florida-LSU, Kentucky-Mississippi State, and Ole Miss-Vanderbilt. Out of those 6, two to three are not really rivals (depending on how you view the Florida-LSU series). Those two to 3 are Kentucky-Mississippi State, Arkansas-South Carolina, and Florida-LSU (again see previous note).
In the wake of Missouri coming to the SEC finally being official. The proposals I've seen have the Tigers in the SEC East, the conference keeping an 8 game schedule with (6 division games, 1 protected cross-division rival, and a rotation of the other 6 cross division teams to fill the last spot), and the (one that I find still up in the air) Missouri playing Texas A&M every year as protected cross division rivals.
There are two methods of thought for Missouri regarding who they want to play as a cross division every year. There's the let's play Texas A&M and then we can recruit Texas and Florida theory. I for one find this to be rather illogical, because their games will be on in Texas regardless if they play A&M every year or not. Besides, they still have 4 non conference games to schedule, 1 going to Kansas, 1 going to Baylor (TX), and possibly the other to Illinois.
The other line of thought is Missouri and Arkansas share a geographical and potential historical rivalry already rooted here, just untapped. Some of the best rivalries in college football are the so-called Border wars. Which Missouri already has with Kansas and Illinois. Why not Arkansas? Going this route would mean that at least one of your conference games is a short trip down the road, albeit to Fayetteville ... but it will allow Tiger fans to feel smarter every other year.
If this plan happens the obvious question is then, who does Texas A&M play? This is where things get interesting. If A&M is given South Carolina, you will have two teams furthest apart play each other every year. While it would be a good competitive game that the Gamecock fan base would welcome with open arms (as it would extend their recruiting into Texas), one would have to wonder how well a rivalry could be maintained with such distances for students and alumni to traverse.
The other option has a bit of intrigue involved. Texas A&M against Kentucky would feature the two schools legendary coach Paul "Bear" Bryant coached before heading to Alabama. While not as much of an intriguing match-up, Kentucky and A&M have not been that far apart in terms of on field success in recent years.
To this I give you the poll.