For now, I'm a Prime member as well, and I use it, so I might as well take advantage of the photos. Not sure if I'll always keep it, but it's "free" in the sense of no additional cost, if you're already doing that. They have a 5GB limit for videos, which we ran out of very quickly, but no limit for photos.

Meanwhile, if you have a Pixel phone, which my wife and I both do, Google provides infinite storage for photos, as long as you back them up in "high quality" instead of "original quality". The quality is generally good enough for my purposes, so I effectively have unlimited photo storage on both Google Photos and Amazon Photos.

Google's unlimited photos (for Pixel users) also doesn't cover videos. We take way more photos than videos, but one individual video can end up occupying a lot of space, so we've hit our limit and had to go back and delete stuff several times. Given that the limiting factor on our Google storage is the videos, and Amazon's storage has even smaller limits for the videos than Google does, Amazon's service doesn't help much with my storage limits on Google. It's nice that I get unlimited quality on Amazon, but it doesn't help with the quantity limits in any meaningful way.

Definitely some of that stuff is specific to me, though, so if it helps much more for you, more power to ya!