I think you should go with a 29 gallon long or tall.
I have a 20 gallon long, and I have one angelfish now, he killed his other friends
He is about 2-3 inches from his nose to tail, and about 3-4" from bottom fins to dorsal fins.
He's growing now

I just have to find him a female to mate with soon when he gets big enough.
I can tell you, that you can keep 2-3 angels in there for as long as they live. I have some angels in my big 500 gallon, and they are HUGE as large as the ones in the wild. They are 10-12" from nose to tail and 14-15" from bottom fin to dorsal fin (top)
Yeah they are big
Don't worry, just get a small or medium sized fish, and keep it in the 29 gallon, you can have a bunch of fishes in the tank if you want, just don't put too many because the angel might think of them a dinner because some fishes don't get as big as angels.
Oh and DON'T EVER put them in with Piranhas. Piranhas eat angelfishes for breakfast, lunch, and dinner in the wild and sometimes it could be vice versa. Angels can kill Piranhas, if the piranhas aren't big enough.