Spectra s1 or Spectra s2

Ny`Shalah
I have decided to choose the Spectra breast pump over the Medela because Medela breast pumps have open systems. However, I can't decide whether or not to get the Spectra s1 or Spectra s2? My insurance will cover both. I'm only 21 weeks so I don't have to let my insurance company know for a few months.