The decision is tough because the offerings are not equivalent.
Google Photos shares storage with other Google services, Gmail and Drive. So, backing up photos to Google can get expensive. Google does offer unlimited photo storage for photos under 2048 pixels on the largest side. So, you can set up auto backup to upload at standard size. The photos will be resized prior to upload. Going full size would eat up storage.
The cost of Google storage is currently $1.99/mo for 100 GB, or one level up is $10/mo for 1 TB. This is the problem I have with Google, the jump from 100 GB to 1 TB. If I could step up in smaller increments, I might be less hesitant.
Compare that to 1 TB free storage at full resolution with Flickr, undoubtedly a great bargain. What if, however, you ever want to store more than 1 TB? It's possible you could get a Doublr account with 2 TB of storage for $499/yr.
To further confound things, we are talking about the new Flickr. I was, and still am a Flickr Pro subscriber, which means that I have Unlimited storage so long as I maintain the subscription. Therefore, the real comparison is unlimited 2048 px photos with Google, or unlimited full-size photos with Flickr.
For now, I've compromised by setting my Google backups to resize my photos to take advantage of the unlimited option. And, Flickr is set up to back up at full-size, even with the cap.
Practical Vs Theoretical
In practical terms, 1 TB is nearly unlimited storage for my photos. I currently have just over 10,000 photos on Flickr, using only 0.028 TB. Flickr calculates that I would need nearly half a million full-size photos to approach the 1 TB limit. I saw a calculation somewhere that states I would need to store 500 photos a day for 80 years to get near that limit.
My hard drive has all my DSLR photos, including RAW files, which amount to 178 GB. Actually, that includes 1080p video too. I don't know exactly how much storage I would need for photos alone; but, it would certainly be way less than the 178 GB. I am inclined to think that perhaps I should cancel the Pro subscription...except that "What if?"
Cognitively, I know that I likely won't reach 1 TB; but, what if I do? I'd like the option to store more.
Flickr should be sufficient storage for all my photos in my lifetime with 1 TB. This puts the Google offer of unlimited storage in perspective. Yes, it is totally unlimited storage; but, we are talking about smaller photos, which would only use up a fraction of my storage on Flickr for the same photos.
Let us also remember that the cost of storage keeps declining, so perhaps somebody somewhere will be giving away 10 TB.
Theoretically, I shouldn't worry about a limit I may never reach nor about storage prices that continue to decline. I could very well be worrying about nothing.
What About RAW files and Video?
Good question. I have another service, Bitcasa, with which I am grandfathered into the unlimited storage plan like Flickr. That is where I plan to keep my RAW files and video along with my other data. My media is going there simply for the sake of redundancy. Although cloud services are magnitudes more reliable at backing up data than I am, it could not hurt to diversify a little.
If I were to hunt around for cloud storage for RAW and video today, I would go with Pogoplug, which is $5/mo for unlimited storage. The added bonus for Pogoplug is that they offer local storage and backup products as well.
Looping back to Flickr Vs Google+ auto backup, I guess I'm doing both at different image qualities.