Since you will likely be using a digital backup of your own physical disc, the quality of the dump is vital. The best practice is to use a "1:1" or full ISO that is exactly in size. A clean dump should match one of the known MD5 checksums for a verified disc.
The "best" ISO is a completely vanilla, untouched dump. If the ISO has been pre-patched with other mods, custom music, or regional translation hacks, Project M's code injections will fail. 4. Legally and Safely Obtaining Your Brawl ISO super smash bros brawl iso for project m best