Stinger - https://en.wikipedia.org/wiki/FIM-92_Stinger

  Mass 
   Missile – 22 lb (10.1 kg)
   System – 35 lb (15.7 kg)
  Effective firing range 
   0.16–8.05 km (.1–5 mi)
  Warhead weight 6.6 lb (3 kg)
  Maximum speed 745 m/s 

Piorun - https://en.wikipedia.org/wiki/Piorun_(missile)

  Mass 
   16.5 kg (36 lb) total
   10.5 kg (23 lb) missile
  Operational range 
   400 m (1,300 ft)–6.5 km (4.0 mi)
  Warhead weight 1.82 kg (4.0 lb)
  Maximum speed 660 m/s

There is no credible basis to believe the Piorun has a better seeker. Piorun's seeker uses a design similar to obsolete variants of the Stinger.

Modern Stingers share a guidance package with the AIM-9X Sidewinder and, unlike the Piorun, have dual mode imagers that work in both IR and UV which makes them impervious to flares.