Backup Time: It will take the least time.
Differential Backup: Backup of the files, which are NEW or CHANGED Since LAST FULL Backup.
Backup Time : It will take more time compare to Incremental Backup.
Comparison : Incremental Vs Differential
Differential Backup it is middle stage between Full Backup & Differential Backup.
Main Difference is Incremental take backup from Last Backup. Differential take backup from LAST FULL Backup,
FULL BACKUP: Complete Backup of everything.
Backup Time: It will take more time rather than DIFFERENTIAL BAKUP.