According to Wikipedia, Sea Harriers shot down:
9 IAI Daggers (Mirage V equivalent)
7 A-4 Skyhawks (plus one write-off on landing)
1 Mirage III
…and 3 other aircraft
No Sea Harriers were lost in air-to-air combat, although 6 were lost to ground fire and accidents. The same page claims 28% of Argentinian air losses were caused by Sea Harriers.
The general view was that the Dagger was faster, but the Sea Harrier more manoeuverable. I remember at about the time there was much press fuss about the Sea Harriers’ viffing ability (vectoring in forward flight). They’d end up with a fighter on their tail, angle their V/STOL engine nozzles to brake suddenly, the Dagger would overshoot and the Sea Harrier would have a clear Sidewinder or cannon shot.