As of 2010 Seagate external drives are pretty good but, they have one feature that is a problem. The FreeAgent drives are programmed to sleep after a short time of non-use. This causes problems with Apple Time Machine and other backup software, where the drive will not mount and be available for the software to do it's job.
To solve this problem, Seagate has a utility that will turn off this feature. Download and install this utility. The installer does it's job automatically and once installed there is nothing else you have to do. It will modify the firmware of the external drive.