Sand v surf. Sand because you will not flip instantly due to the lift you still have at the beginning of your roll out and aerodynamic control. OTOH if there were people or obstructions to hit on the beach I would prefer surf. When a light aircraft ditches the vast majoirty get out so the question is then how likely are you to drown? Just off a beach, it stands to reason that you will most likely be ok. But I would rather use the beach even if it was likely to result in parking upside down.