NASA gives contracts to ATK, Dynetics, and Northrop Grumman for the advanced booster for the SLS.
Dynetics is the group that is proposing the F-1 powered boosters. ATK is of course sticking with solid fuel. Seems like Northrop Grumman is just developing the fuel tanks for the booster. So it is pretty much down to ATK's SRB's and Dynetics F-1 powered boosters. Go Dynetics.
http://www.nasa.gov/home/hqnews/2012...iR0LE.facebook
EDIT: Ha. Got NASA's social network people to respond on Facebook saying that safety is their number one goal for SLS after trashing SRB's.