[Yggdrasil]

Well, you get interactions between the bromine and hydrogens when the methyl is equatorial.  I'm not sure how the size of a methyl compares with the size of a bromine.

[RBF]

According to published "A values" (a measure of 1-3 diaxial interactions), the bromine atom (A = 0.38-0.49) is considerably less sterically demanding than the methyl group (A= 1.70).  A list of these values can be found at the following link:

http://www.chem.wisc.edu/areas/organic/index-chem.HTM

You will need to select "A values" from the list at the left.

[Yggdrasil]

Sweet.  Thanks RBF.  So, saN, you are correct.  The preferred conformer will be the one with the methyl group equatorial and the bromine axial.