I've been playing with voice over IP for over 10 years. Business use for the past 7 years and I have not had a land line in my home for almost 4 years. I like Linksys hardware (SPA2102) It gives me two lines.
My current provider is voip.ms and I'm happy with the service. Phone numbers are $1/month. Calls are about a penny a minute, toll free numbers are no charge. When I travel I set up an extension and call home for free. Too many features to discuss. Voip is a bit of a hobby and things can get complicated. Biggest call quality factor is latency. Voip does not need much more than 120Kbps but the packets have to arrive reasonably quick (~50ms latency) or quality deteriorates. If anyone in your house streams video or uses torrents it can cause problems.
I've never used Skype, but any solution that involves a PC (USB phone) is at the mercy of the PC. I've found the call quality inconsistent.