Easy for me to keep: monti digis, encrusting, and plating, millis
I acquired these later and have managed to keep them alive: crayola table, german blue polyped green acro (ORA), Oregon tort, some sort of other tabling acro
What I have thought to be hard (from reading around or in my experience): anything deepwater, acros in general (the wild ones or ones that just generally look like they'd be hard), I cannot keep a birdsnest if my life depended on it
Generally picky corals either from my experience or locals: purple monster, sunset monti (some pieces can be a PITA while others are ok, all are the real deal), one particular piece of rainbow monti (could be from a bicolor blenny though, not positive), superman digitata are not necessarily a pain to keep, but they change colors depending on if they're happy or not
Things that were hard for me might not be hard for other people because unlike a lot of SPS keepers I do not have a calcium reactor, nor do I have an sps only tank (lots of zoas and other corals in with them). In addition a water change is a rare thing for me (I'm about to get flamed for this one...) but for the most part I'm doing pretty good with keeping colored sticks alive.