Snugpak is a brand name and offers a variety of different sleeping bags. If I recall correctly, they're all synthetic-filled vs. our issued down filled ones -- big advantage of most synthetic filled bags is they will retain heat better if wet; down-filled bags have better insulation:weight ratios and compress better (depending on type & quality of down used). With a Snugpak, you'll be able to choose between a (proper) mummy bag or a rectangular -- if warmth is a key concern, then I recommend mummy. If you're a taller or shorter dude, you can get one properly sized for you.
I find most issued bags have been beaten down into mere nothingness and have had a few without any down in a couple of baffles at all. You may not be able to get your QM to dry clean a non-issed bag, but that's something I find happens all too often, anyhow. And should you have a problem with the sleeping bag in the field, such as 20 litres of diesel, CQ may not let you do an exchange.