For me is better to have a schema that you can map directly to code (easy to automate), mainly because code is what is going to be at both ends.
GET /orders <---> orders
POST /orders <---> orders.push(data)
GET /orders/1 <---> orders[1]
PUT /orders/1 <---> orders[1] = data
GET /orders/1/lines <---> orders[1].lines
POST /orders/1/lines <---> orders[1].lines.push(data)