This question should not be answered too hastily. Just a few months ago, FireWire, with its 400 Mbit/s, was much more superior to the USB interface. In this respect, the fact that you have to by a FireWire controller is actually not too painful, especially considering that the drive itself sets you back about $350. The current USB 1.2 standard, however, has no future when it comes to the gigabyte area - the data transfer rate is much too slow.
USB 2.0 could be the alternative because it offers up to 480 Mbit/s, and is backwards-compatible, as well. Up till now, however, even though its future success as a standard is already ensured, USB 2.0 is not yet widely established. So at this point, if you're in the market for an external drive, you're going to have to by a corresponding controller, whether you opt for USB 2.0 or FireWire.
This is where Western Digital steps in: controller cards for FireWire cost about the same as those for USB 2.0 cards. Also, FireWire is the undefeated champion for videos, and it still offers the ambitious user the better advantage. We can also expect that, starting from the end of this year, almost all PCs will come equipped with a USB 2.0 controller. So, if you opt for FireWire now and plan to buy a new PC soon, you'll have both of the interfaces to play with in the future.
The Drive: High Quality
With a size of about 22 x 15 x 4.5 cm, the FireWire drive is as big as a tupperware container, and it weighs approximately 1.3 kg. These are quite acceptable figures for this much storage space.