Both have very similar monthly fees. Both are cloud gaming services. Having tested both, I noticed that the latency is excellent in each. There’s no lag or anything like that.
I think the only difference I noticed is the following: In GeForce Now, to play any game, you must own it in your Steam, GOG, etc. library. In Luna, if you don’t own any games, you can still play some games without needing to purchase them. In the Standard plan, you have access to games like Hogwarts Legacy, Resident Evil 2, Borderlands 3, Skyrim, etc.
Not to mention the option to stream via Twitch without needing a high-end gaming PC for it. A perk that the GeForce Now audience has been asking for years, but is now available on Amazon Luna.
In the end, both are very good services that work; they have their differences. It’s still hard to choose, but I think I would go with GeForce Now since I already have many games on Steam. Luna is still very new and has many games that are not yet compatible.
Having seen what happened with Google’s Stadia, I prefer to be cautious with new services. Even though they are very good.