All kinds of approach. Some choose by brand preference, considering given brand as superior in quality. Others will consider any ram that is compatible and has good price per Gb. And some others will mostly look after superior specification (like lowest possible latency). Pretty much depends on what you need - if you are limited by budget, naturally your best call is to look for best price per Gb. If budget is not a factor, going for most reliable brand is probably most often used tactic.
But in the end, pretty much all ram sticks work the same. What matters more is to decide how much ram you need, what speed and how many sticks -choosing brand and model is only second step here.