Why is the effect of beta-branching neglected in this comparison of SN2 reaction rates? Which compound would give a faster SN2 reaction?
  
  
  2-bromobutane
  1-bromo-2-methylpropane
  


The answer is given (2).

While I agree that the primary position is preferred as compared to the secondary position (for an SN2 attack), but won't beta branching hinder the nucleophile's attack, hence, reducing the reactivity for SN2?
Yes, the beta branching will hinder the nucleophile a bit, but the substrate is still a primary halide with 2 hydrogens on the carbon that is attacked. The steric effect of having a methyl group and a hydrogen on that carbon vs two hydrogens is very much larger.