Good question. Google has a good offering with Google Photos, but if you are interested in storing full resolution photos at low cost, then Myra Cloud is the clear winner. You get 5 times more free space and when you run out, Myra Cloud is still about 3 times cheaper.
Another reason you might prefer Myra Cloud is that Google Photos is just so feature heavy that it is very slow and seems no longer to be about your photos. Myra Cloud is focused on giving a FAST browsing experience, even on low end laptops.