I go for the turn option. Reasons:
*Most likely to have traffic tracking same track below you. Inertial navigation is frightening for having everybody on the same line over the ground. A rapid descent could give TCAS a real test- turning onto a random heading will ensure less conflict that remaining on original track, so get off the centreline.
*Nosing over straight ahead will cause significant loss of 'g'- whilst the cabin crew and people standing are trying to move. A big turn will reduce the loss of 'g' as you nose over into the descent.