To really truely tell the sex of your angel fish you need to look at them while they breed.
I only know that the males tubes is slightly pointed and the females tube is roundish. But I forget what the tubes are called. But I'm just saying what I've heard, so I could be wrong...
I've noticed that the egg tube on my female angel fish is always out just a little bit, and the males is not. But that is just because she is old enough to breed, and has eggs inside her... I think.