no method is more difficult than the other one, they are all the same... easy
i personally prefer to load my games from the internal hdd, i believe some games do not even load from an external hdd because you cannot copy files that are bigger then 4gb on an external hdd.
the method you choose will change the folder you have to replace the update.img file, im not 100% sure but when you load the game from disc or from external drive, you have to replace the update.img file either in the patches/install data folder which is: dev_hdd0/game/YOUR GTA GAME ID HERE or in the folder which your backup itself is: dev_hdd0/GAMES/
you have to try it for yourself, i cannot help you more here, because i use the method below
when you want to load the complete edition from the internal (like i do)
you need to follow this guide:
http://www.ps3iso.com/ps3-tutorials/...-internal.html and you have to replace 2 more files,
for the modloader you now have to replace the update.img file in the dev_hdd0/G/E01128/USRDIR/update/ folder
EDIT: here is the complete edition internal fix reupped by me:
http://www.mediafire.com/download.php?m3b1553wz93c703