The iMac has faster components. The CPU, not such a big deal. The GPU? There is a huge difference. The Macbook Pro has a 6750M with 1GB of vRAM, while the best you can get for the iMac is a 6970M with 2 GB of dedicated vRAM. However, if you're going to be gaming, the MacBook Pro is a much better choice. The lower resolution will allow you to run more games at native resolution than the iMac's massive 2560x1440 native resolution. It all depends on what configuration you're getting.