Is skype the best voip service provider or three are others voip service providers? ?

I would like to have a Voip service provider. Which is the best option skype, power phone, google phone, etc ?.

Related posts:

1. How to make international telephone calls to India using voip service, is there any provider for free service?
2. How to make international telephone calls to Inida using voip service, is there any provider for free service?
3. How do I use Skype and another program to make free VOIP calls to landlines?
4. How is the call quality of VoIP? What are the best providers?
5. What is soft voip and how is it different from voip service like skype?