The difference between primary and second research collection is that primary research data collection involves conducting research oneself, or using the data for the purpose it was intended for. Secondary research data, on the other hand, was collected by a third party or for some other purpose.
Primary data can be collected by someone in the organization. This person has to have a clear plan for conducting research, including specific research questions and methodology. The data that is collected is used for its intended purpose.
Although there are many different ways to classify designs, one that gives a clear overview of the various procedures is based on three methods of generating primary data: experimentation, observation, and survey. (enotes, see first link)
Secondary data might actually be the product of other research, or might have been collected by someone else. Unlike primary data, secondary data is not tightly controlled by the researcher. The process has already happened, or the data was collected for a different purpose.
To determine the data sources for the research project, an assessment must first be made of the amount and type of data presently available. These data are called secondary data. (enotes, see first link)
Which data you use depends entirely on your resources and your purposes. Each has its benefits and drawbacks.