FlightAware used to be stronger in North America, FlightRadar24 used to be stronger in Europe (and generally anywhere outside of North America). That's still true to a certain extent, but both networks have been filling up gaps of coverage in each other's continents.

I actually use both; they complement each other well. Let's cherish that there is some competition in this field.

IIRC, FlightAware is quicker to make assumptions about flight statuses that may not always be true, so I'd give the benefit of the doubt to FR24, especially if the latter has a receiver that is tracking the flight. Although I would consult other sources of information to be sure.