Never kept any other corys but my bronze wernt hard...just sorta...happened...all with the conditions/environment im guessing im not a fish breeder but get stuff right for whichever one and theres nothing stopping them.
It's not a matter of some corys being hard to breed and others being easy, it's a matter of getting them well conditioned and then having the environmental conditions they require just right. In this respect some breed more readily in a typical aquarium environment than others do. There are some that nobody have been successful with breeding yet.
If you are thinking about trying to breed your first corys, I would recommend either bronze or albino C. aeneus. C. paleatus or C. panda would also be good choices.