What's Best for Backups: External Hard Drives or Remote Backup Service

I have a RAID5 NAS. Grab an old PC if you have any lying around and check the motherboard for how many SATA connectors it has. Throw linux on it and run software RAID.

I have a build like this on an old PC with 6 SATA ports. One has a 500GB system drive for Ubuntu linux, and then 5 2TB drives in the remaining 5 SATA ports. One of the 5 is for parity, so the total capacity is 8TB and it can survive the failure of any 1 drive. If one fails, pull it out, slap a new one in and the array rebuilds automatically.

The computer/NAS is connected via Gigabit Ethernet and my editing PC is too through a Gig-E switch. I am getting writes from the editing PC to the NAS of more than 100MBytes/sec.