I'm curious as to why you need our opinions as to what YOU should keep?
I only kept fish that I liked and I wanted to experience keeping. THAT'S all that really matters. ( BTW I have kept many varieties of fishes, because I wanted to
Whichever you choose, set up the tank appropriately for that specie. No, not all Rainbowfish will do well in a 55, but some will. Yes, if you have a larger number of Angelfish and 2 of them decide to pair off, there will be some fighting going on in the tank and you will be better off either keeping the pair by themselves or removing the pair from the rest of the fish. Lowering the number of Angelfish reduces the chances of creating pairs, but it's not a guarantee. Sometimes people get lucky ( or unlucky depending on the outcome you want) when they get just 2 fish.
The main thing is to choose the fish YOU like and treat them appropriately. If you can't make up your mind, I suggest you get nothing until you do. This way, you will have what YOU want to keep and enjoy having.
It would be a shame if you kept something that someone else wanted you or suggested you keep and it turned out you didn't really like.
You just need to learn about the fish before you get them to make sure they are an appropriate fit for your setup.
So the big question is " Which do YOU like, Angels, Rainbows or both? "
Hope this helps