Incremental Backup
Unlike full backups, incremental backups check first if the file modification time is more recent than its last backup time. If this is not the case, the file has not been modified since the last backup and can be skipped. If the date of the change is more recent than the last backup date, the file has been modified, and then you can run the backup.
The primary advantage regarding the use of incremental backups is represented by the fact that the latter are faster than full backups. The primary disadvantage is that restoring any given file may mean to perform one or more incremental backups until the file is found in the question. When restoring a complete file system, you must restore the last full backup and every subsequent incremental backup.
Differential backups
Differential backups are similar to incremental backups and then they modify only those files. However, differential backups are cumulative, in other words, with a differential backup, once a file is modified it continues to be included in all subsequent differential backups (until, of course, the next full backup).
This means that each differential backup contains all files modified since the last full backup, making it possible to perform a complete restore with only the last full backup and the last differential backup.
I know you consider that the differential backups tend to increase over time (assuming different files are modified over the time since the last backup). This places differential backups somewhere between incremental backups and full in terms of use of the backup support and backup speed, while often providing faster single-file and complete restore.
So given these characteristics, I believe that it is better to consider the differential backup.