I've had a Western Digital 400Gb mypassport drive for about a year now and I thought it was great at first but I think it's now finally giving up the ghost. The connection from the hard drive to the USB cable is a bit flakey. At the moment I'm having to jam something under the cable so that it's at an angle with the drive to get it to work at all.
I was thinking about replacing it with a Buffalo although I haven't had any experience with them before. I'm definately not buying another Western Digital...they just don't seem to be very well made.
Sorry for such a late reply but thank you for your honest opinion. I have chosen to buy the Buffalo external hard drive and so far it has been without problem and it comes with a 3 years warranty. A great buy in my opinion.