I wonder if some of the apparent confusion resides around the terminology we're using.
Here are three different sleep systems, all set up in "bag configuration. The two on the left are true "bags" in that they have a hood and a zipper. The one on the right is technically a "quilt", so in fully cinched "bag" configuration, it relies in straps instead of a zipper. It's also BYO hood.

This is the middle "bag" and the "quilt" opened up in use as, what I would technically call a "top bag" configuration, as the footbox is still fully enclosed. The Arc Quilt in question is of this type, although the bag on the right is a true "quilt" in that it can be completely opened flat.

The red bag will have a zipper along each edge, and some extra material in the hood region, but otherwise acts exactly like the bag on the right. It also has a differential cut which helps it to hang better whether zipped or opened flat as a "top bag".
This is the true "quilt" in full quilt mode

The bag on the left in the first photo is a "bag", but only has down on the top, and half a zipper, so can NOT be used as a "top Bag" or "quilt" under any circumstances. Restless side sleepers do not like this kind of bag!
So which is best? Full Bag, Half Bag, Top Bag, Quilt? I mostly use the half bag these days as I am a solid back sleeper so I can take advantage of the great weight to warmth ratio offered by this system. Side sleepers and restless folks should avoid this type of bag like the plague, and will need to carry a less efficient quilt or top bag to get the same warmth (or bag that can be used as a quilt, like the red bag). There clearly is no BEST except what wors for you.