in hot/warm weather I sleep in just shorts/t-shirt and I use a 45* 3/4 length synthetic UQ.
down to about freezing, I wear longsleeve top and bottom baselayer and maybe fleece at night, and use a shorty (48") 20* Down UQ.
below that I still do the baselayer and maybe fleece but use a full length Down UQ.
this is what I do, not saying it's what anyone else recommends...