Hard to tell, it depends on things like your skills or your goals, both short and long term.
I personally preffer Unreal. A year ago you had to pay $1500 + $1500 + $1500 for Unity to get the full toolset for PC and mobile. And even though you don’t have to pay it to start working with Unity now I do not regret the choice.
I love the Blueprints system, it allows me to easily experiment and do stuff that I could not do alone in Unity just like that. I don’t have the time to learn C# before even starting to have fun with games. With BPs I can gradually learn what I need at the moment and move forward with my ideas in the same time.
I like the looks of UE4, the lighting and shading model, and I simply love the material editor with it’s workflow and it’s creative possibilities.
I can also say that the community and staff, both here on the forums and on answerhub are a huge asset of UE4. I have nothing but positive experience in using UE4 social tools.
I do also strongly believe that the mobile development will get all the needed improvements, and choosing UE4 I did understand that this is a new tech, especially the mobile support.
And mobile games are not my only interest, I have many different ideas and plans for the future that are more suited for UE4 than Unity IMO. And I am saying that after playing around with Unity for some time.
But if you are only interested in mobile games, and you are a skilled C# programmer I guess that your point of view would be quite different.