You have a minimum hight or clearance to achieve. That said, once you determine the clearance you are faced with shorter bunks on a narrow stance or taller bunks on a more broad stance. Also consider your working depth if you are tidal high bunks may have you waiting for water at low tide.
Go as wide as you can for ease of settling on the lift and stability once lifted. If the hull has stakes avoid lining the bunks upon the strakes for a couple good reasons.
1) Small boat strakes tend to thin, weak and not backed up.
2) On wide bunks the hull will level itself nicely if resting on the hull flats. If resting upon the strakes it's easy to a little stuck crooked sometimes.
Oh..... and nice legs.