I had all sorts of acros in my 14 gallon that did fine. I would avoid monticaps as they can really become dominating in a small tank. I would also avoid very thick SPS like spaths, albros, some stags, and the like, just because they need to be a certain size for them to start to look like a colony, and in a small tank, you cannot give them enough running room without crowding something else out. Stick to smaller branchier species because even as "minicolonies" they still look nice. Tables are another coral I would avoid for the same reasons above.
From a care standpoint, nothing you can't keep alive in a nano.