I'm so confused to choose these laptops

Solution
1. It's difficult to render a definitive opinion without a real-world listing on e.g. Amazon or BestBuy. But you can go over these 2 reviews to get a better idea:
a) From notebookcheck, June 2017:
https://www.notebookcheck.net/Asus-VivoBook-S15-S510UA-i5-7200U-FHD-Laptop-Review.226200.0.html

b) From trustedreviews, August 2017:
http://www.trustedreviews.com/reviews/lenovo-ideapad-520s

2. These laptops are very similar and I don't blame you for being confused. From what I can tell, battery life is about the same - which is not very good, at 5 to 6 hours. The Lenovo is slightly heavier, but this may prove a blessing in disguise: the reviewer at notebookcheck noticed that the ASUS tended to 'bulge' on the bottom cover when the laptop was...
1. It's difficult to render a definitive opinion without a real-world listing on e.g. Amazon or BestBuy. But you can go over these 2 reviews to get a better idea:
a) From notebookcheck, June 2017:
https://www.notebookcheck.net/Asus-VivoBook-S15-S510UA-i5-7200U-FHD-Laptop-Review.226200.0.html

b) From trustedreviews, August 2017:
http://www.trustedreviews.com/reviews/lenovo-ideapad-520s

2. These laptops are very similar and I don't blame you for being confused. From what I can tell, battery life is about the same - which is not very good, at 5 to 6 hours. The Lenovo is slightly heavier, but this may prove a blessing in disguise: the reviewer at notebookcheck noticed that the ASUS tended to 'bulge' on the bottom cover when the laptop was doing heavy work. This indicates lesser-quality materials and lower build-quality overall. In other words, the Lenovo may be heavier, but the extra weight does give you a sturdier chassis. For long-term ownership, this is worth considering.

3. In my opinion, the ASUS is the better-looking machine. It offers a good screen, but it isn't a true IPS panel. The flimsy bottom cover does worry me, and it's something I've never come across with any Lenovo. The Lenovo is certainly stylish, and the reviewer at trustedreviews praised the keyboard in particular. It's heavier than the ASUS, but I would actually consider that a plus because the Lenovo is unlikely to bend or bulge as described above. Finally, the Lenovo comes with an actual IPS panel, and while this panel is part of the reason for the mediocre battery life, it's definitely worth it.

4. I'd choose the Lenovo.
 
Solution