There are potentially a few different ways in which a LiteSpeed backup can be performed, which are as follows:
1. LiteSpeed Backup Database Wizard through the Enterprise Console
2. Maintenance Plan
3. MMC Console
4. Script through Query Analyzer
Depending on which method is chosen for backing up the database, there will be some difference in the size of the backup files.
There is no best option to choose that results in the best settings available for backing up a database. Whichever option is chosen for backup, there is going to be a difference in the file size created. The procedures and threads that run to create the backup file are most likely to run in different configurations every time a backup is performed.
Also the first backup performed is always going to be a little bigger than the next because it is in effect two backups wrapped into one file. First, SQL puts a mark in the transaction log and backs up all data pages, then SQL backs up from the log, from that mark. If you do two full backups, back to back, the first one will almost always be bigger, due to the extra data in the transaction log.