[brucepick]

My thinking is, a block heater puts its heat right into the engine where you need it. Alternatively, the kind that installs into a heater hose would probably be a close second.

If you live in REALLY cold country, or if you live in kinda cold country and drive lots of short trips where the car stays cold for a high percentage of the drive time, one of the above would probably be a good idea. Service shops and parts stores in those areas are familiar with those heaters.

The other solutions, while clever and they help, lose a lot of their heat to the environment. So, not worth the effort.

The electric blanket might get around the heat loss issue if you put an insulating blanket over it to trap the heat. But if you actually LIVE in cold country, I doubt that you'd make plans to fool around that way on cold mornings. I live in Connecticut, and the last thing I want to do when it's 10 degrees out and I need to get to work, is fool around with the car. Get in, turn the key, and go. Fastest way to warm up is to drive it.

You do get better mpg out of a cold car by EOC: engine off coasting. It takes longer to warm up that way, but overall mpg is higher over any given distance, measuring from a dead cold start.