It depends on your preference towards the Operating system. I suggest you to try both phones before purchasing. Even though I use an Android phone, I admire my friend’s Lumia 730 as it’s display is awesome with perfect viewing angles, no lags and a good design and build quality. Also iPhone 4s is a bit too outdated now. I vote for Lumia 730.
Nokia Lumia 720 is a better option when compared to iPhone 4S. The Lumia 720 gets a bigger 4.3 inch touchscreen with 480×800 pixels. The use has been eased with the introduction of Windows 8 mobile to the phone. It gets a bigger battery, higher camera resolutions and a better price tag for the overall practicality of the phone. The iPhone wins when it comes to screen resolution and full HD recording and playback option.