Until today I would have agreed that the Dell Inspiron 7559 is the best for under $800. However, that's no longer the case.
HP has a 4th of July sale that ends about July 9th 2016 for which they price dropped tons of laptops. One is the
HP Pavilion 15t. Base model ($570) has a 1TB HDD, i5-6300HQ, and GTX 950M 2GB. However, it can be upgraded to any combination of the i5-6300HQ or i7-6700HQ WITH GTX 950M 2GB or GTX 960M 4GB, plus they only charge $60 to swap the HDD out for a 256GB M.2 SSD. That means for $710, you get almost the same exact hardware as the Dell (15-6300HQ + GTX 960M 4GB) with the only major differences being:
61.5Wh battery instead of Dell's 74Wh
DDR4 2133 RAM instead of Dell's DDR3L 1600
But wait, there's more, because the HP Pavilion 15t, is as its name implies, touchscreen capable for another $70. And if your budget isn't quite so tight, $850 gets you the i7-6700 and GTX 960M.