So to answer your question, the links provided in the alternate download sources, is the fastest (for most players) download source, but you Can download the game through the GamezBD-Launcher as well it just takes more time, regarding the resume-downoad ability, pretty sure both of them do, so it is just up to you to test which is faster for you specifically.
I can say that using the alternate download link has a massive advantage over the Launcher, first up if you use the Torrent download that means that you can always start and stop the download without any trouble, and it has the added benefit that you can save a copy of the game somewhere else, so that you will not have to re-download the game again if something should happen, however you will need a Torrent-download-client, I can recommend Tixati just because it is the most simple client without any useless additions.