If you mean shrubs then I'd advise getting as much of the old stump out as possible first. Its a pain but it sounds that your shrub died of a disease from the way you described it. As the garden is west facing then most plants will work. Depends what you are looking for really.

I wouldn't plant another Buddleia there though.....

Buddleja can die of old age but the most likely reason is mould that has attacked the roots, such as Pythium or Phytophthera sp.. Buddleja don't like wet heavy soil in winter and these pathogens can cause slow death; peeling bark is a sure sign of these diseases. If I am wrong and the soil is dry then vine-weevil grubs can weaken the roots as well.
Don't plant anything there for a year and try to improve the soil with compost and lime/gypsum. Anything that is able to attack a Buddleja will probably be able to kill the next plant.
I think the aspect is relatively unimportant in this case.