Mine was my dwarf gourami, even though I would never own another one. He had so much personality and is the whole reason I'm now obsessed with fish. It was great having him at work for company and he always made a stressful day better.
I'm also very fond of my hengel rasboras- they're just such pretty little fish. And the ghost shrimp make me laugh when they muscle the cory cats out of the way and steal their wafers. And of course I love my betta- he's so funny at feeding time because he gets so excited he just swims all over the place and won't come to the top. And my sparkling gouramis are gorgeous and have such vivid blue eyes...
I guess I love them all!!