VoIP to VoIP
I'm using VoIP at home through Vonage, and while there was a time that I was having bad luck with it, since I switched ISP's, I haven't had a single call whose quality I haven't been happy with.
Something occurred to me a couple of days ago - at work, we use Cisco VOIP phones. This means when I call home, I'm talking VoIP to VoIP. And the calls sound great.
I'm still not ready to fully commit to Vonage at home; I recently switched my Bell line to to Roger's "Home Phone" service, based on PacketCable. No problems with that so far.
At home I'm using a Uniden two-line cordless phone, which is perfect for fence-sitters like me - I can use my Rogers line or my Vonage line from any phone, with only one base (all the handsets communicate wirelessly with that base).