Individual drippers are useful if you want to water an individual item (i.e. something in a pot), or control the amount of water delivered to a plant (some may need more than others, and there is a good choice of adjustable drippers where you can control the flow of water).
If you're watering a small bed, it's easier to use a drip line (the pipe contains regularly spaced outlets to release a fairly consistent amount of water), as it's easier to move around and cheaper/less hassle than individual drippers. It's also cheap/easy to install a valve which will let you control the flow to the drip line for the bed so you can turn it on/off (as required) and adjust the flow so you don't over-water the bed (which can be a problem with soaker hoses).
If you run a main supply line to the areas you need to water (mine's 13mm), and then calculate the number of fixings you need (elbow joints, t-pieces, shut off valves etc.), it's easy enough to attach individual drippers or drip line (mine's 4mm) as required.
AM :-)