Personally the hardest angel I've kept is a Bandit (arcuatus). It took me 3 weeks to get it to eat but now it readily accepts ON angel formula and NLS pellets. Luckily, it just took a while for him to get used to its new surroundings. With the harder to keep angels, the difficult thing is getting a healthy specimen to begin with and getting it to accept prepared foods. I have kept an emperor, passer, french, queen, annularis, regal, and blueface (not all at the same time obviously). I would have to say the passer and emperor are up there in terms of aggressiveness, but the french I had was pretty passive. The blueface and regal were extremely shy, along with the annularis. It also depends on how big the angel is when you receive it and what order you want to add them in as well. As for the genicanthus family, I've had no trouble with either the spotbreast or the semifasciatus as both began eating immediately in qt. Just my 2 cents.