Head gasket would be chugging white smoke all of the time especially when you accelerate not just at startup and you'd definitely have some more symptoms like running hot. There's always bubbles in antifreeze sitting at the top of the radiator and coolant tank, its when its actually bubbling when the car is running that you know you have a problem. If it was a head gasket you'd have water in the oil or coolant coming down the side of the block. I would bet that your problem is bad valve seals or worn valve guides and that puff of "white" (blue) smoke is just a bit of oil that dripped down into the combustion chamber. Valve seals are dirt cheap and a piece of cake to replace. Start there.