Which is better in MongoDB? Storing a list of members as a array in an object or member group relation collection

I am building a social app with MongoDB. I have a scenario where I need to store the list of users in a group and their relation to the group. What is the optimized way to store it? I had come across 2 paths.

• Saving the list of users inside the group collection

  {
    "groupId":"",
    "admins":[
      "1234","2345","3422"
    ],
    "moderators":[
      "3242"
    ],
    "members":[
      "2354","9865","6747"
    ]
  }
  

• saving group id, user id, relation as a list in a separate collection in traditional style

  {
    "groupId":"1234",
    "userId":"8764",
    "relation":"Admin"
  },{
    "groupId":"0987",
    "userId":"4345",
    "relation":"Member"
  },{
    "groupId":"0987",
    "userId":"3456",
    "relation":"Admin"
  },{
    "groupId":"0987",
    "userId":"7654",
    "relation":"Member"
  },{
    "groupId":"0987",
    "userId":"8765",
    "relation":"Member"
  }
  

  My major Queries would be to

• list the members of the group with their relation

• search the members by their starting word

• list the groups a user is a member of

Which approach will be best suited for the above quires.

** excuse me for the json formatting is not accepting in the editor code style.