From your initial post I assumed you were a photographer, and were simply looking for the best format to use when returning processed images.
If you're trying to sell (self-store) archival services then M-DISC is certainly one way to go, not least because it makes all those 1000 year claims on your behalf.
The graphic on their website...
Image
...strikes me as nonsense, though. A DVD written once on a domestic burner
might be good for seven years, although I'd imagine that a very significant percentage will be unreadable after that time. But the claims that hard disk (spinner, presumably) and a flash drive are good for only 5/8 years respectively is absolute rubbish. Write once then put either of those in your sock drawer for fifty years and I'd be amazed if the data was gone. I'd be even more amazed if your sock drawer M-DISC was still good after a century.
In reality, the best anyone can really hope for is a storage medium that's still 'good' at the last date anyone is likely to attempt to retrieve data from it. One thing that CD/DVD/M-DISC does have going for it is that it's more platform neutral than a HD or flash drive, and the means of reading such discs is likely to remain more readily accessible than will be the case for GUID/NTFS etc.
Personally, if confronted with a 3.5" floppy or a ZIP drive, I'd most likely throw it in the bin unless I was damn sure there was something very valuable to me on there. But an 8" floppy? Or a SyQuest 44MB? The time and effort and cost, and the hoops you'd have to jump through, in order to try and retrieve anything meaningful from those would be ridiculous. But they *were* storage 35 and 20 years ago.