oplocks - or opportunistic locking - is only of importance when multiple simultaneous access to a file is required - situations where, just for example, the same file is going to be accessed from two locations at the same time.
If the file is only going to be accessed by a single user or process then you can use either setting.
MAP archive relates to the mapping of the file attributes across the two different file systems (in simple terms - the DNS-323 uses a linux based ext2 file system and you are accessing it through SAMBA to make it appear as a Windows based NTFS file system) - Windows uses an archive bit which linux does not have.
This is of more importance to a back up application which will use the archive bit to determine whether or not any given file should be backed up or not, when doing differential and/or incremental backups. For backup I would set MAP archive ON.
NOW - if you are backing up your files using ftp the MAP archive bit setting may have no effect - I don't think traditional ftp clients will pay any attention to it.
Edit...
Edited to preserve the content after censorship.
Mr Moderator - perhaps you should review the acceptable word list - take a look at the paragraph below and see if you can figure out what is so offensive about it that it deserves to be censored.
Here's the original paragraph.
This is of more importance to a back up application which will use the archive bit to determine i***iven file should be backed up or not, when doing differential and/or incremental backups. For backup I would set MAP archive ON.