No such thing as "better". While they both offer streaming services, they are different enough that I don't consider them as an either/or. For a long time I had both, but I realized we watched Netflix so seldom it just wasn't worth keeping it, especially with the last price increase. With Amazon, we pay for prime anyway for the shipping service, so I consider the streaming "free". Also, Amazon offers titles for rent or sale, while Netflix is solely streaming what is in their catalog. All of my digital movie purchases are available via Amazon, but not all of my 4K titles are actually available from Amazon in 4K. But since I can also get the same digital titles via Vudu, Google Play and Movies Anywhere, I have plenty of choices.
If you are interested in any of the Netflix original content, then it becomes a non-issue. You have to subscribe to see that content. Same with the Amazon original content.
Nvidia Shield, Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.