In reply to ParaDan:
There’s no such thing as a straight answer here.... apart from down as opposed to synthetic.
It all depends on whether you run warm or cold, what you will wear inside the sleeping bag, expected minimum temperature, how fit you are, budget, how much you are prepared to carry etc etc.
If really struggling, a 4 season-ish down bag should be ok.
Have a look at the Mountain Equipment bags, there is a decent description of what activity each is suitable for.
Post edited at 09:56