The main reason I chose Crashplan+ Family Plan is because it can cover unlimited GBs on 10 computers. This means I can backup nearly everything on all of my Mac and Windows computers. I should mention that I am not backing movies up via Crashplan and that is mainly because I plan to use Walmart's Vudu service to put them online in a higher resolution, but I haven't got around to it yet.
One of the main issues with backup services is the amount of time that it takes to upload data via the internet. I have more than 1.5 terabytes that I needed backed up and that can take a year or more to backup via the web.
With Crashplan+, you have the ability to use their Seed Kit to backup files quickly. The Seed Kit costs $124.99 on top of their normal plan pricing. They send you a terabyte drive that you can plug into numerous computers (one at a time) and run the Crashplan program to back them up. It does some sort of encrypting and compressing, so it probably holds closer to 1.5 terabytes of your data. Once you are done, you simply send it back in the same box using the prepaid label they provided in the package. Be aware that if you go this route, you should not back up anything else until they have notified you that the files are finished being uploaded to their site. The Seed drive will overwrite anything you have backed up, so make sure you decide if you want this service when you initially sign up for the Crashplan service.
With the Seed service, I was able to back up three computers and an external hard drive that contained all of my ALAC (Apple Lossless) music files and all of the photos I have taken over the last 9 or 10 years.
The other benefit is that if you have a major issue and need to restore 3.5 terabytes or less of data, you can pay $164.99 to have a drive shipped to your door. If I needed to restore tons of data, this would beat spending months or years waiting for everything to download from the web.
Crashplan also has an iOS (iPhone) app that I have used. It currently requires the file to be downloaded to view/play on the device, but it does work. I would prefer being able to just stream it from the web or view the photo file without downloading it first, but it does work if you need a file from your backed up computer while you are out.
I should mention that I have read a blog that the writer discussed how Crashplan lost his entire backup by a combination of a corrupt drive and human error. Crashplan, according to his article, says they have fixed this oversight, but I would warn against using them or any online service as your only backup. It is best to have multiple backups. I plan to have everything backed up on a NAS (when I get one), as well. If you want to be really careful, Crashplan will also allow you to backup to a friend's computer.
There is a great book on the ins and outs of Crashplan if you want to read about their block-level incremental backup methods, encryption method secure keys, and more. I have read a good deal of it and I have found it very useful in understanding the service. You might be able to hunt down most of the information on Crashplan's website, but I got the book on my Kindle which helps with searches.
If your needs are similar to mine, I would recommend Crashplan+ Family Plan. It costs $124.99 for the Seeded backup and 13.99 a month if you pay on a monthly basis. It is significantly cheaper if you pay for a year or more up front. They also have cheaper options, if you only need to backup one computer. For me, it was the perfect answer to my backup needs, but I will update if I run into any issues.