I'm not sure that there is a "best brand" for PSX backups...
Personally, I like to use generic Prodisc and Ritek media because it is unbranded and therefore easy to make a nice label for, and the quality is well within the amount needed for a PSX
Smartbuy is the brand used by Prodisc, but the newer Prodisc looks like it has problems. The 32x and 24x stuff is fine if you can find it though. Ritek media can be found in some 48x TDK media, most if not all Maxell 40x media (not Maxell Pro), and their housebrand Ri-Data, which is VERY difficult to find in most places.
don't forget you need a mod-chip, and must own legal original copies of the games you intend to backup.