Most will recommend a block-level backup. Theoretically, bl0ck-level backup is utilising less bandwidth and storage. Block-backup can only backup block that part of the file is modified, thus it is using less space. If you are using block-level backup and VSS is enabled to backup a Microsoft Windows Server, you can back up an open file. The file-level backup will fail in this situation. If you have a lot of small files, file-level will take a very long time to backup them. Block-level is especially suitable for this type of situation.
However, file-level is not useless. Actually, the backup allows you doing both. The file-level backup is flexible. You can choose the files and folders to backup. Especially, those don’t need to backup frequently, this can be a faster restoration option.
Either a block or file-level backup, backup is a must in case you need to roll back or restore.