It is not a case of better, it is a case of you use the boot-time scan when avast detects something in normal mode that can't be dealt with, e.g. the file is in use by another program, or protected in some other way.
Deletion isn't really a good first option (you have none left), 'first do no harm' don't delete, send virus to the chest and investigate.
There is no rush to delete anything from the chest, a protected area where it can do no harm. Anything that you send to the chest you should leave there for a few weeks. If after that time you have suffered no adverse effects from moving these to the chest, scan them again (inside the chest) and if they are still detected as viruses, delete them.