Suggest between Dell 7520 and Dell 5521 laptops?

[Suryaprakash]

Hi, i am looking to buy an official laptop to make it use as a personal as well as for official use. And as per my budget constraint i came to finalized two laptops which i found better and also i am preferring dell because dell laptops are very good. I wan't to know that between these two Dell 7520 and Dell 5521 which one should i buy please read my constraint first and then suggest
1. It should have a powerful processor.
2 Must support 2 GB of more RAM
3. Battery life must be up to 3 hours.
4. It should be good in looks'

Please tell me as soon as possible. thanks in advance.