Different tools for different jobs IMO. I own down bags, synthetic bags, fleece sleeping bags, fleece blankets & wool blankets.

One nice thing about the fleece or wool blankets is that they store relatively compactly for long periods of time. I'm reluctant to compress a good sleeping bag for months at a time in order to keep it in the car without taking up half the trunk. I can keep a couple of inexpensive fleece sleeping bags (or wool blankets) in the trunk using the same amount of space that one synthetic sleeping bag would occupy. Now, when it gets really cold I'll throw a down or synthetic bag in the trunk but I won't keep it compressed too long without giving it a break and lofting it back up.