none is better, if you consider game compatibility they are identical (they use the same boot code).
if you consider features (downloading covers automatically, having an internal nintendont updater, having a specific look or interface, etc.), then you choose based on the feature you want.
here you can compare the 4 most known loaders.
https://gbatemp.net/threads/backup-loaders-comparison-chart.333364/
some features might be missing, this chart is old.
CFG Loader is maybe a little old, I don't know if it works with latest version of Nintendont.
Latest addition to USBLoaderGX and Wiiflow is "WiiU WiiVC Mode", to use the loader's interface on a WiiU gamepad, only to launch nintendont ! no USB is possible with this feature.
No idea if PostLoader is still maintained.