Another way to ask that question, is where should your records reside? That will determine which Bishop is charged with watching over you, including giving you the interview for your temple recommend for living ordinances (assuming you're being sealed in the temple). Also, if any issues/questions/concerns arise, that will determine which Bishop is authorized to meet with you regarding these types of items. Since as russellhltn states the Handbook allows for either YSA or family wards, I'd suggest you meet with one or both Bishops, and discuss with him/them your situation, and seek their counsel as well.