I've have both bags and quilts.

My two favorite sleeping bags are Big Agnes models, one rated to 30F and another rated to 0F. As noted previously Big Agnes models have a sleeve on the bottom into which one inserts a pad. I've used both closed-cell foam (CCF) pads, inflatable pads, and the combination of both. When I used to sleep on the ground I preferred the an inflatable pad and used a thin CCF pad beneath the inflatable pad as puncture protection and additional insulation.

I now sleep in a hammock and have switched to quilts. I have a Golite Ultralite quilt rated to 20F that weights 1.5 lbs. It works very well and I could easily use it lower than the 20F rating. I also have a Jacks R Better Sierra Stealth quilt rated to about 45F that weighs 15 oz, and I made a lightweight quilt (about 16oz) using Climashield that is good to about 53F. For temperatures above 30F I tend to use my two lightweight quilts combined and they work very well together. It is these two quilts I now use on bike tours -- modular system of synthetic and down that weights less than 2 lbs and works well to at least 30F (I have not yet tested below 30F).

One poster mention that with quilts there is no head protection. When needed, I wrap or drape my jacket and/or a shirt around my head and neck. I've used this method below 20F and it works well for me.