I angel will do fine in a tank as the only fish, or the only angel, provided you have the proper tankmates. Anything that has longer, flowing fins will probably be seen as an angel, and treated as such. This usually means aggression problems.
I've been keeping corys & bristlenose plecs with angels for a long time. The juvie angels are actually more bothersome to them, adults ignore them unless protecting a spawn. Plecs are egg eaters, and will try to munch on a spawn. They will get nipped, but being armored cats show little effect.
I've also kept numerous livebearers with angels, kribs at one time, and have a few angel fry in with a batch of apisto fry. I'm sure there are a few I'm forgetting.