IPhone 4 vs Nokia Lumia 520?

Right, for Christmas i can either get a Nokia Lumia 520 or my sisters iPhone 4, its a couple of years old, just wondering which would be better all around?

I have got both and definitely stick to iphone device

If the condition is good, I would personally advise you to go for the iPhone all the way. It outmatches the Lumia 520 by a long shot. 520 is good but you can definitely not compare it to the iPhone 4. Windows is emerging as an OS but iOS is way ahead. BTW if you have second thoughts about both of 'em, I'll suggest you to get a Motorola Moto G (Priced similarly to the 520)