I think the best option is to find fish that you think are beautiful, aren't too hard to take care of, and that aren't too expensive. I don't know about you, but for me that would be widebar silver dollars, bichirs and geos. I also have datnoids. With expensive fish like black aros or stingrays, you'll always stress about them and you lose some of the fun in keeping them. but I don't really stress about my geos too much because they only cost me like $15 each and they're big already and pretty tough too. Same thing with bichirs. I try to buy fish that cost less than or around $30 that I know are tough and that I think are really nice to look at. If you keep buying bigger fish just to impress or one-up your friends, then it never ends and you can never sit back and enjoy the fish you already have.