Ethernet WAN modules

Hi

I am thinking about testing a new Ethernet WAN services. What are your experiences with such services, especially compared to the most common Serial services (Frame Relay, T1, T3, FT3)
What does one gain? Lose?
Are the Ethernet WAN features the same as in Serial?
What are your experiences with Ethernet WAN interfaces on Cisco Routers?

Your replies are most welcome

Lesly