I've used LaCie Quadra hard drives previously and have always been impressed with them. The v3 3TB is no different and works a charm with the new iMac. Very easy to set up - took 5 minutes and the in-built menu talks you through the process. Backed up the mac very quickly using USB3.
Usually sturdy build and feel to the hard drive, plenty of cable length and the drive backs up very quietly. Overall, a little on the pricey side, but I can't fault it and would highly recommend.