D'Fusion gives more functionality than metaio and vuforia but charges of D’Fusion is higher and also need renewal every year. Whereas metaio take charges only once, when we purchase sdk but vuforia is free of charge also for commercial use.
Also, D’Fusion is cross-platform application. it supports web browser, android and ios without use unity, whereas metaio and vuforia supports unity.
Metaio is easy to integrate than vuforia but the functionality of meatio is less than vuforia. Also Image tracking of vuforia is more powerful than metaio. Also, other functionalities which are supported in vuforia is not include in metaio. Vuforia supports Native functions and java for android and natively implemented ios app also supports unity same as metaio supports their native function for android and ios and unity. Metaio develop functionality using AREL which is used javascript, HTML and CSS and we can use this file in all platforms.
You can use metaio or vuforia for Unity3D according to your requirement.