We recommend the use of micro sprays over drip except where the bed or planter is less than 50cm wide. Micro sprays provide a more even coverage for smaller plants and in dense planting areas. Micro sprays tend to provide more even watering of the whole root zone. If the bed is narrow (or a self contained planter) then a drip pipe may be better. Be warned that unless the soil has a high clay content the water will not spread out from a dripper pipe more than 10" or so. In sandy soils this may be even less.
Visit the Evergreen Irrigation Ltd website for more information on I have a narrow shrub bed I want to water, should I use drip pipe or micro sprinklers?