The major product of 1,4-pentadiene NBS bromination
The Main reason for looking at the stability of the intermediate is Hammond's Postulate. Now the intermediate has the electron density spread all over it's body. SO it's reasonable to look at the activation energy of the transition state itself.

When the Br radical attacks at the end position, you have a much sterically favored transition state and the other two bonds are in conjugation and hence we would expect the activation energy would be much lower for this and not for the other transition state where the Br attacks at $3^{rd}$ position. 

Hence we can conclude that conjugated diene is most probable product !.

Please correct me if I am wrong.