I'm going to buy one of them
1) Acer V5-571G - 2Gb nvidia , i7 2.0GHz , 6gb for 750$
2)Dell inspison 15r - 2Gb AMD , i7 , 4gb for 770$
3) Dell inspiron 5537 - 8GB DDr3 , 1Tb , 2GB ati radeon VGA for 800$
now my question is , which will be better overall and for gaming .. I'm not a hardcore gamer but will it be enough for lowish-medium settings for games?
It'd help if you posted links. We can't do much from such vague information as "2GB ati radeon VGA". That's like inquiring about renting an apartment and only being told that the building exists somewhere within the United States. But chances are those PCs are crap. Not so much the Acer, but likely the Dells. Anyway, your best bet is Lenovo.
The cheapest one will do very nicely for gaming at medium or high settings, and some low settings in more demanding games.http://shop.lenovo.com/us/en/laptops/ideapad/y-series/y510p/