Laptop A will perform better for gaming. It's gpu is definitely better. You should be able to play at medium-high settings, depending on the game, at 720p resolution (1366x768).
From experience, my old hp i5-430m with an AMD HD5650 mobility gpu could play crysis at medium-high settings at 1366-768 with 30+ fps. The cpu in laptop A is a little better and the gpu is also a bit better.