Depending upon environments ... live server -> test server and the specs of test server, one of the easiest and most reliable ways is to use rsync for all of it ... DB, code, and data directory. Initial rync will take time, but if one runs the rsync again where what's new gets xferred and what's been removed gets removed on test server, it's fairly short time to wait.
Git and CLI is definely more reliable ... IMHO ... git dependent upon how much one might have customized site (hacked code, etc..) The the CLI upgrade is best me thinks as it takes Apache out of the loop ... just php and your MySQL/DB server then ... even if that DB server is a dedicated box.
Have one server right now that resides on a CentOS 5 server (true standalone) which has only 2Gig memory. Have already rsync'd all of it to new server that has same version of CentOS but more memory, faster processor, etc.. When it's current environment can't handle the load, I think I'll be able to get the site migrated in less time and more accurately. New location already has virtual apache config for it and it's just a matter of final xfer via rsync and changing DNS. Since I'm anticipating this migration to be called for in a reactive mode, I run the rsync scripts once a week now. And use 'stealth mode' access to the new location to check it. So far ... no issues on testing.
'spirit of sharing', Ken