Advantages are
Easy to learn and use;
Faster iteration time;
Better cross-platform integration is available with Unity.;
Unity engine has great support for 2D games, while Unreal is more 3D-centric;
Unity has a more active community;
Huge amount of assets ready to use;
Disadvantages are
Its tools for graphics are average. ...
Its built-in support for PhysX lacks major functions. ...
Its best features need expensive licenses. ...
Its source code is inaccessible. ...
Unity consumes more memory.