Spectra S1 and S2 breast pump

After a long search noticed that many moms do not recommend Medela or recommend Spectra over it.

So for moms who have used the Spectra breast pump, which do you prefer S1 or S2? What is the difference between them? They seems very similar. Is it easy to clean? Can I use other bottles for it such as Philips Avent or Boon nursh?