Vuforia is great on the technical side. Their cloud API is responsive and their tracking is strong, but their documentation is terrible. Look up Vuforia Swift to see a starter code on how to use it on iOS. They have well structured examples, but it took me a few weeks to understand how everything works. What type of AR are you trying to build, cause there are Marker based AR and SLAM based AR.
For Pokemon Go style, I think Unity might be the best option, but I don't take my word for it.