Check out REI’s wide selection of sleeping bags
Our family has a variety of sleeping bags in our collection, and they all have distinct characteristics. If you are planning to use your sleeping bag for backpacking, there are decent weight savings to be found by spending some more money. A 20 degree down fill bag we recently purchased shed about 3 lbs of total pack weight, and is actually warmer than the heavy bag it was replacing. We also have two synthetic bags of similar weight and temperature rating; however, one compresses much easier than the other. Seeing and examining the bag in person before purchase is probably a good idea before you spend your money.
The temperature ratings should also be treated as a “ballpark” measurement as well. Construction, materials, quality, and your personal comfort levels will all determine how a bag feels at a certain temperature. Temperatures at night on my Arc Dome trip dipped down into the 20s. My 20 degree bag actually felt cold in some spots. Luckily I brought plenty of insulating clothes to sleep in, effectively raising the comfort level of the bag. From my experience, a 20 degree bag seems to be suitable for 3 season camping, making it a good all-around bag. I just unzip it or sleep on the top if it’s too hot. And when camping in the high elevation mountains, I’ve never been too hot come early morning.