What do you plan on doing with the laptop? The dual core is faster.
But, if you are multitasking, then the quad core will be even faster because it can do more at one time and retain a certain speed. While the dual core can do things quickly, but once you load more and more at one time, then it will slow down incredibly to be able to split the performance onto each running process.
Dual Core: Faster, good for gaming, browsing the internet.
Quad Core: Slower, good for multitasking, rendering, hard-tasks.