[Link: en.wikipedia.org]

I have used B most of my career, phone guys like A. Seems like most modules nowadays are preconfigured in A to line up with phones.

And once again the only difference between A and B is the the pairs are swapped. It makes no difference with baluns or anything else!! If you have issues with A and you switch to B and it works that means you f$cked up your termination the 1st time.