Storage Account Contributor role versus Storage Blob Data Contributor

DK 

The difference between the roles is in the "dataAction" of the Storage Data Contributor.

The Storage Account Contributor has no dataActions permissions for the storage account, however, it can do everything that's not data. Including SAS tokens.

The Storage Data Contributor can Generate SAS tokens for blob using the Microsoft.Storage/storageAccounts/blobServices/generateUserDelegationKey action.

Scoping the Contributor role to the storage account would of course give you the same permissions, but not best practice according to the least-priviledge approach for RBAC.  

Azure Build-in roles permissions: 

Storage Data Contributor

  "permissions": [
    {
      "actions": [
        "Microsoft.Storage/storageAccounts/blobServices/containers/delete",
        "Microsoft.Storage/storageAccounts/blobServices/containers/read",
        "Microsoft.Storage/storageAccounts/blobServices/containers/write",
        "Microsoft.Storage/storageAccounts/blobServices/generateUserDelegationKey/action"
      ],
      "notActions": [],
      "dataActions": [
        "Microsoft.Storage/storageAccounts/blobServices/containers/blobs/delete",
        "Microsoft.Storage/storageAccounts/blobServices/containers/blobs/read",
        "Microsoft.Storage/storageAccounts/blobServices/containers/blobs/write",
        "Microsoft.Storage/storageAccounts/blobServices/containers/blobs/move/action",
        "Microsoft.Storage/storageAccounts/blobServices/containers/blobs/add/action"
      ],
      "notDataActions": []
    }
  ]

Storage Account Contributor

"permissions": [
    {
      "actions": [
        "Microsoft.Authorization/*/read",
        "Microsoft.Insights/alertRules/*",
        "Microsoft.Insights/diagnosticSettings/*",
        "Microsoft.Network/virtualNetworks/subnets/joinViaServiceEndpoint/action",
        "Microsoft.ResourceHealth/availabilityStatuses/read",
        "Microsoft.Resources/deployments/*",
        "Microsoft.Resources/subscriptions/resourceGroups/read",
        "Microsoft.Storage/storageAccounts/*",
        "Microsoft.Support/*"
      ],
      "notActions": [],
      "dataActions": [],
      "notDataActions": []
    }
  ]

Contributor

"permissions": [
    {
      "actions": [
        "*"
      ],
      "notActions": [
        "Microsoft.Authorization/*/Delete",
        "Microsoft.Authorization/*/Write",
        "Microsoft.Authorization/elevateAccess/Action",
        "Microsoft.Blueprint/blueprintAssignments/write",
        "Microsoft.Blueprint/blueprintAssignments/delete",
        "Microsoft.Compute/galleries/share/action"
      ],
      "dataActions": [],
      "notDataActions": []
    }
  ]