I agree that leaving a disk spinning will make it last longer. Startup/shutdown puts a bigger load on disks mechanically, thermally, and electrically. I, however, also shut down my FreeNAS regularly because of the electricity bills. Mine's just a simple home setup (4 disk RAIDZ2 in a quad core XW4600 workstation), so there's no need to run this system 24/7. I chose ZFS for it's focus on data integrity, so if my disks will wear out earlier because of my regular shutdowns i expect to retain my data without problems...and if this means having to buy a new disk a bit earlier than usual, so be it...good excuse to slowly upgrade to a larger capacity :)
For disk recommendations...hmmm, i always stick to Seagate disks. Even my earliest disk still works. Maybe i'm lucky, but so far no Seagate has failed me, in contrast to other brands.