Since ARFoundation is free, I'm thinking about using it on a project. What I need is only Image Tracking. But I have a few concerns:
1-) Vuforia supports almost any mobile phone with a camera. I remember, I was using it even in early 2014. If ARFoundation is mainly a framework which is a combination of ARCore and ARKit, I have concerns about it. I know ARKit supported on iPhone 6 Plus and later (fair enough), how about ARCore? Can I trust it on mid-tier Android phones released on late 2014 or more? Can someone define the trade off here?
2-) Implementing Vuforia on a Unity project is a piece of cake. I have a limited time. Would you bet on ARFoundation on a project? Is it "stable" enough or do I have to google it to work, like there's no tomorrow?
Edit: After a 6 months long project development, I have something to say: Use ARKit for IOS, and Vuforia for Android. This way, you will have less headache on Android and more power for AR in IOS :)
ARCore is supported in a lot of devices but still exists a (really) big gap between the ones that works and don't work. You can check all supported devices here: https://developers.google.com/ar/discover/supported-devices
You can see that is missing really a lot of devices from before 2017-2018. Also, it's very important to know where do you plan to release your app, some countries probably have more users with the latest phones.
Lastly, Vuforia is really easy to add to a project, really really easy. ARFoundation is not really dificult, but it is not as easy as Vuforia, but it is stable, it's awesome. It's just a bit more complex to understand, but that is not really a problem, there are a lot of samples out there. You can start with the official ones: https://github.com/Unity-Technologies/arfoundation-samples
If you want just marker based AR, stick to Vuforia. If you need more complex experiences using AR Planes it's better to use AR Foundation.