What's the best filter for a 15 gallon tank?

I have a 15 gallon tank with 2 goldfish in it. Right now I have a Tetra Whisper filter but I'm so fed up of it. This is the second one I've bought and less then a week after changing the bag the water starts to just trickle out of it. I've done everything from taking it apart and cleaning it out completely to turning off the filter when i feed the fish, it still wont work. From what I hear Aqua-Clear and Bio Wheel's are pretty good. Which is best?