I personally like Wiggy's bags. They are heavy and can be bulky depending on the compression system, but unlike down they will keep you warm even when wet, have a lifetime guarantee and can stay compressed indefinitely. Machine washable to boot.

If you are looking for a car bag I would especially get a Wiggy's, as their only downside is weight. That said, I have no real problem carrying them around under a ruck anyway, but they are definitely not for the ultralighter types.

Keep an eye out for sales on their website as you can often find great deals.

Greg