Lumia 720 vs 820

Hi,

I am planning to purchase my first smartphone and I need a suggestion from you guys, that out of lumia 720 and 820, which one should I buy?

(I am well aware of the fact that 820 has 1gb ram + 1.5Ghz dual core processor.)

-> Criteria :

1) Camera

2) Built quality

3) Screen quality

THANKS!!