It depends on what you're studying in terms of what is more reliable to use.

Secondary data often uses much broader levels of evidence gathered by multiple sources and examined by a variety of experts and can be very helpful if you want to know things like demographic trends in an area, areas of industry change and growth, and about what platforms are more or less effective in spreading specific messages. However, secondary data is often not specific and may not tell you a lot about whether your particular service or good will succeed or not, when it comes to questions like this, you would be better served by conducting primary research about your specific good or service.