When it comes to WAN connections for companies, I have heard of MPLS, BGP, T1, in addition to Site to Site VPN (Which I think it is not considered as WAN)
From Companies Network Engineer perspective
With MPLS, I believe the MPLS provider will configure the Customer Edge router then connect the router to the company Network, the engineer of the company does not have to configure anything.
With BGP , I am not sure what needs to be configured at the company level.
The same with T1 Line
Site to Site VPN is configured from A to Z by the company engineer as long as the company is connected to Internet.
Anyone to clarify on this question?