There are a ton of VoIP solutions on the market. We deal with a broad range of them on a daily basis. For the most part, they all have mastered a clean and easy to use interface. They all offer call quality that is as reliable as the network they run on and you can choose from a wide range of phones specifically geared to your needs and budget.
So what separates a good VoIP provider from another? For us the answer is price, support, and contractual commitments. The big names in the market (some of whom are publicly traded companies) excel in one out of three (hint: support). But they often lock you in to long term contracts that are at the same price point as a traditional landline.
That's why we love OnSIP's service. They are a month to month, friendly, easy to use VoIP service that hits all three of our criteria for a phone provier. Their support is amazing and they only charge $24.95 per month for unlimited calls! For those offices that don't need infinite minutes, they offer a per-seat metered option to help you manage your costs. They have a slew of customizable apps like auto-attendants, dial by name directories, conference bridges, softphones (no hardware required) and many more. Full disclosure: OnSIP is AD.Visory's phone provider and we love what they do.
You can find out more about OnSIP on their homepage.