Assuming you are in India, the price difference is about four thousand. Both are great devices (especially when you consider the prices), but it all comes down to what you are looking for. The internals are similar. The differences are few. 720 has a 4.3 in screen, as opposed to 3.8 in screen on the 620. 720 uses IPS LCD, 620 uses AMOLED. 720 has more pixels in both cameras compared to 620. And 620 does miss out on an FM radio. If the FM radio is not important, and you're ok with a smaller screen, go for the Lumia 620. Else, get the Lumia 720.