For me it depends on a number of things:
*Shape desired of the plant
*Size desired
*Foliage needs (color, shape, etc.)
*Time of bloom (can be influence on time of year such areas/plants will be seen)
*Sunlight- the the CA Central Vallley it is quite different than the nearby Sierra or Bay Area so I need to be cautious as to recs on "full" or "part sun."
~Scott