If you are looking to buy a new rug I would go with a MW - you will probably get more use out of it during the year. I don't actually buy HW rugs, just stick a stable rug under her MW and it is just as warm.
Taz is still double rugged he's that cold and he's only chaser clipped he's in a full neck hw in the field with a medium weight under rug and in the stable the same but with no neck as its a different rug lol and we're only in edinburgh