I d recommend going with down if your are wanting compressibility and light weight. The higher the fill longer life you ll get and the more comfort you will get from your bag, though high-fill down is pretty expensive. When I was living in Sudan I used a 20 degree Marmot synthetic. I did nt care about weight and compression, and it worked well. In the summer just sleep on top of it, in the winter zipped it up around me and was toasty. The advantage with synthetic is cheap. There is also the issue that down sucks when it gets wet, while synthetic does not suck as much when it gets wet.
Anyway, dont worry so much about brand name, as long as its a company that will back up any defects (manufactures warranty), and it fits your reqs and budget.
Ohh and one other tip: I always take like a really wide bed sheet and fold it in half and sew it together. Its like those cotton hostel liners you can buy.