How is the call quality of VoIP? What are the best providers?

I am thinking about switching from Cox to a VoIP provider. I have had Vonage and Sunrocket. I loved Vonage, but then I heard about Sunrocket and it was cheaper, so I switched. Sunrocket was horrible, so I switched back to Vonage and it was really bad. I switched back to Cox and that is what I have right now. I am thinking about AT&T Callvantage, but they don’t have an agreement to transfer numbers from Cox. Would it be worth it for me to transfer my number from Cox to Verizon and then to Callvantage or should I find another VoIP provider? If you think I should find another provider which one should I switch to? I live in Rhode Island.

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