Read the many many threads here in addition to the tutorials.
The only one even in extra is slackpkg, so it'd get a semi-official nod, but I've never used any of them. Read the ChangeLog, download the packages, upgradepkg. What do I need a third-party tool for that for?
But all of them have their friends and all of them have some user who'll tell you it borked their system. Except the manual method, where you know *you* borked your system if anything goes wrong.
But, sure, try 'em and decide.