G'day Joshua,

Good question, it would really depend on how you plan on using the hood. If you plan on using the pillow inside the hood then the smaller Aeros Ultralight Pillow will work better, but if you need to close the hood up around your head for warmth then either size will work as you'll need to use it outside of the sleeping bags hood. I use a large and really love it but I'd struggle to fit it inside the hood of my bag.

G'day Paul, 

So I've tried this with the Latitude LtI that we have on display (but the hoods should be the same across the Latitude range) and I found that the Aeros Ultralight Large fits snugly in the hood of this sleeping bag.