I'm getting my hair dyed tomorrow for the first time in years! I'm naturally a dark blonde, but I need some lighter blonde highlights so the increasing number of grey hairs I've got sprouting from the top of my head look a little more blended!

The question is--do I go for full or half head? I've had both done previously and I can't remember which looked best! What are the pros and cons--apart from the cost, which isn't much anyway?