Do they use the same data sources/aviation services? If so, how do they differ?
2$\begingroup$ It really isn't in the scope of this site to evaluate outside services. $\endgroup$– Ron BeyerMay 2, 2017 at 17:00
$\begingroup$ I'll answer anyway - flightradar has a network of receivers ( flightradar24.com/add-coverage ) to process transponder and Flarm signals $\endgroup$– gusto2May 9, 2017 at 10:25
1$\begingroup$ It cannot be closed for "opinion-based", as the main sources are well known (ANSP, private ADS-B receivers network). It may be broad though. $\endgroup$– minsJun 19, 2017 at 8:35
$\begingroup$ @mins, well it got closed for asking which one was better. (and anyway, personally I am not sure it is on topic) $\endgroup$– FedericoJun 20, 2017 at 8:06
https://www.flightradar24.com/how-it-works - taken from the FR24 website. They use ADS-B - hence the reason the majority of General Aviation stuff doesn't show (unless it has a mode S transponder).