Nstive (swift / java)
Reasons:
- You can do customizations easily (In big complex app you simply can not go
for cross platform due to lack of customization)
- Plenty of resources are available for [Android Tutorials]
(demonuts.com) and iOS tutorials.
- You can build UI Layouts and programming classes with full control in
developer's hand.
- Complex app will have future expansion , this is where customization and
native scripts will actual play it's role.