In the end it comes down to the software that you are running and on what processor. So if I running a single threaded app like Plants vs. Zombies the fastest processor will make the difference even if it is a dual core. On the other hand if I am running something that is multi-threaded then the best results will come from a quad core most likely.
Which core i3 and what quad core? What are you doing? If you plan on browsing the internet, the i3 will most likely be the best, as it is pretty fast per core.