Appreciate this is not an exact science but curious as a fair discrepancy here.
I have a Pi running PiAware, I also feed FR24 and ADSBx.
Earlier today I checked some statistics and noticed that Flightaware showed 717 aircraft spotted whereas FlightRadar24 showed 673 - a difference of 44 aircraft which is around a 6% difference.
Both are enabled for mlat - I do appreciate times data is processed may be a factor too.
As many FA enthusiasts also share data to other ADS-B trackers curious as to other views on data comparison.