I have a 55 gallon tank at home and since im moving (YET AGAIN) i'm going to have to empty it and fill it up again obviously

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So I was wondering. Which fish should I get? An oscar or two or a few Angelfish? I love them both, but it just wont work well with both.
Angelfish I like because they are VERY beautiful fish and even though they aren't 'solitary' fish they are a really nice addition to the tank. They also will make the tank look full. (Unlike now, where I have about 5 gouramis, an eel and a ghost knife). Also they pair themselves off which would be pretty cool to see then bond with another mate. Also I can have them with other fish such as certain tetras and bigger fish ECT.
Oscars I really enjoy because they are 'solitary' fish and something about them just draws me toward them. They will also fill the tank. While I can add some other cichlids like African cichlids and maybe a jack depsy. I LOVE Electric blue african cichlids and certain colors will fit in really well. At the moment, I currently have two african cichlids with a zebra pattern on them both.
I do have one question...Why does one have an orange stomach and the other doesnt?. They are both the same size and look like 'baby" zebra cichlids.
This is the exact way they look:

And only one of them has that gold/orange looking belly. (Unlike the picture, one of them with the orange/gold has it on both sides and it covers their entire belly). I'll have to get some pictures up soon.
Anyone know a good link as to how to tell male from female?
And this is the EXACT same eel that I bought:
And this is the EXACT same Ghost Knife I got:
Both are still small and I was told that the eel can get up to 2 feet. as will the ghost knife. (I'll find out how much that is true though).
Anyway...What are your thoughts?'
P.S.
I'll get some of my own pictures up soon.