My favorite fish is an unlikely candidate; my 6 year old Albino Cory who, despite my hard water, has bred many times and actually has a surveing 3 year old daughter who has recently spawned as well. Normally the eggs are attacked by fungus or the Gourami pecks the eggs off the glass.
If I had a proper tank I would like an Angel fish and would consider it my favorite individual fish, preferably gold.
It is hard to pick a favorite out of a school of Rasboras but I think a big group of those are magnificent.