I am kind of new to this site, and lately I have been closely observing the "fish" tag. I love fish, and everything about them. I am thinking about starting an aquarium myself, and need to pick out the best supporting fishes for my aquarium. Would asking for help picking out the best species of fish for my aquarium be off topic on this site and the fish tag? (Assuming that I provide the other specific features of my aquarium, other fish, decorations, size, etc...)
Short answer = yes
I would suggest you start by look through our 400+ existing fish questions They should be helpful in getting you started.
You can search for specific things like fish and best (100+ results) where you will find questions like What kinds of fish recommended for my 3 gallon tank? which was not well received but did get good answers.
Best is subjective so, a good question will indicated what limits your choices (i.e. space, time, equipment) The best questions indicate that you looked at existing Q&A and what you still need help with.