Are you saying the SilentX fans are of poor design or the stock fans?
The SilentX fans won't make your tank run any cooler than the stock fans but they will run a lot quieter.
The biocube 14 uses 50mm case fans, search on newegg.
The stock fans are 2 wire while most case fans will be 3 wire. You will have to cut the old adapter off the stock fans and splice it on to your new fans. You will need to utilize the power and ground wires from the new fans. The attached image should help you in determining which wires these are.
You can of course go the led route that convict suggests to help control heat as well and much improve the color and growing capabilities, but for a cheap fix for noisy fans try the SilentX.