I'm not a huge fan of the Penguins, but for that much of a price difference I can understand why you'd buy one. They work perfectly well, I just don't like the cartridges. You can make your own, though, and save money on buying them in the long run. The Penguin is going to be louder than the Aquaclear, if that is a concern.
29 gallon would be a great size for your goldfish. However, I disagree about the sense of urgency in this thread. Is the fish in an inappropriately sized tank? Yes, of course, and I'm not disputing that. But you mentioned that you do a lot of water changes, and if you change enough water in my experience you can squeak by for a while without causing harm to the fish. Obviously you need to upgrade the tank, but the tone of some of the posts here is "OMG your fish are definitely going to die really soon!" and I just don't think that this is probably the case based on the information you've given.
Noise is a concern for me, I have a AC 50 and it's nice and quiet. What I'm worried about is the fish getting stunted, I REALLY don't want that to happen. This is my fav fish I've ever had, don't wanna take any chances. I've found a 30 gal tank with stand on Craigslist and I think it comes with the lights, hood, decor, gravel, and filter all for $40. It's a little over an hour away so I might not be able to get it.