Out of everything I've tried, Clownfish have been the easiest to rear, but as a general rule, the Bangaii Cardinalfish would hands-down be the easiest (provided you don't have a male like mine that routinely eats the eggs). Basically the rest of the Cardinalfish have short incubations and pelagic larvae - the Bangaii is very atypical in the Cardinalfish.
Just my $0.02
Matt