POST parameters on REST api - links or inline?

I am trying to design a rest api and i have a resource with links to another resource. say

GET /resource1/id1

{
  "property1": "value1",
  ...
  "links" : [
    {
       "rel": "res1to2rel",
       "href": "/resource2/r2"
    }
  ]

now on a post to create resource1, i want to pass a relationship to resource2. should the POST call look like

POST /resource1

{
  "res1to2rel": "/resource/r2"
}

or should it look like

POST /resource1

{
  "links" : [
    {
      "rel": "res1to2rel",
      "href": "/resource2/r2"
    }
  ]
}

What is the best practice, should the POST match the GET or can it have properties that you dont see on GET?