Better for gaming?

First one

Mactronix  

First by far, but for that price range an i3-2120 and a radeon hd 7850 would give the best overall gaming performance.

Depends on the game. I would rather trade a bit of easily upgradable later GPU power over ending up with a weak CPU any day of the week.
The 2500K is not going to let you down any time soon, it will handle much more powerful GPU's easily. The 2120 wont.

Mactronix  

If we are trying to future proof then I need to know the rest of the parts he plans on purchasing. But yes I can agree that the 2500k will allow more upgrade room in the future.

Edit:

The rest of the parts will be:

RAM:G.SKILL Ripjaws Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory

HDD:Western Digital Caviar Black 1TB 7200RPM

SSD:Corsair Force Series 3 CSSD-F60GB3A-BK 2.5" 60GB SATA III Internal Solid State Drive

Case:Cooler Master HAF 912 (I'm going to add 2 200mm fans later on)

Motherboard(For the 2500K):ASRock P67 PRO3 SE LGA 1155 Intel P67 SATA 6Gb/s USB 3.0 ATX Intel

CPU Cooler: Cooler Master Hyper 212 +/EVO (I Haven't decided yet).

Also, I will be playing mostly graphically-intensive games such as Battlefield 3, Skyrim, etc.

"Also, I will be playing mostly graphically-intensive games such as Battlefield 3, Skyrim, etc"

Then you answered your own question. BF3 multiplayer is very CPU intensive and the AMD CPU might not be able to keep up. The Intel i3 will also most likely not handle it. Yes I'm speculating, anyone with those CPU's have first hand info?

Gpu is MUCH more easier to replace than CPU's so first build would be more beneficial overall, even if the 2nd one will have slightly higher at the moment FPS(gpus have much higher resell chance than cpus IMO)

A bit late but yes, my friend has an i3-2120 / HD 6870 rig and it runs bf3 on medium like a dream, even in multiplayer. It runs high settings well too if you don't mind 50 fps with 40 fps drops.

No such thing  

mix it:
CPU: i5-2500K
GPU: Galaxy GeForce GTX 560 (Fermi)

Even then... generally I feel that the gpu should always cost more than the cpu in a gaming rig. A 560 ti or an HD 7850 (if you can find one for ~$230) or perhaps a 7870 / 660 ti would be better fit with a sandy i5.

+1

first one