I haven’t seen this posted, but I was on the fence about buying the $ 1.99/month. By paying annually instead of monthly, you can now receive a discounted rate. Never hurts to save a couple of bucks if you already have a pay plan in the first place.

100GB for $ 19.99/year (16% savings) – Comes out to ~$ 1.67/month
1 TB for $ 99.99/year (17% savings) – Comes out to ~$ 8.34/month

Yes, you could just use OneDrive/Amazon Cloudv(unlimited photos with Prime) or other cloud services to upload photos. For me, Google Photos integration with Google Drive and my Android Devices is seamless.