Usually i’d say 2D is faster to develop then 3D Art especially if you’re aiming for 8bit or 16bit style.
For most ppl it’s also easier to learn 2D then 3D modelling, rigging and animation.
Ofc. if you’re a 3D expert, you might be faster with 3D then with 2D.
In the end, not everyone is able to master 3D and not everyone can do good Pixelart.
So i’d recomend you to start with learning either 2D or 3D instead of jumping straight into UE4 without any custom content in your hands.
If you’re good at drawing, 2D might be your best choice.
But if you rather construct geometric shapes on Paper then to draw stuff from your imagination, 3D might be a thing for you.