The last greatest factor to consider in selecting a bag is the insulation that is used in that bag. While both will do the work to maintain you warm, they both have their pros as well as cons. Some kind of extra padding under the bag is very advised.
If you see a +20 degree score that would certainly indicate that the bag should be cozy enough for temperatures that are 20 levels or warmer.. And if you see a - 20 level score then it has actually been figured out that the bag needs to be cozy sufficient for minus 20 degree climate.
An additional kind of sleeping bag is the mommy bag. Unless you are intending a trip to an extremely cold climate and resting outdoors after that you will possibly be happier with rectangular sleeping bags over a mommy style bag. These bags have a certain use as well as they are extremely particular, extremely cool weather condition, mommy sleeping bag.