For gaming i would defently take the i3, this is a dual core vs a hexa-core and the hexa one only wins by a small margin in performance, and that means that the i3's individual cores are much faster, making it's single threaded performance almost double the speed of a FX6100, and it's singe threaded performance you'll wanna look at for gaming.
If we aren't talking about gaming then the FX6100 would probably be my suggestion, since it's overall a little bit faster than the i3, and it's overclockable, while the i3 isn't.
But both CPU's are fine and no matter which you pick it's going to be a good choice. Personally i've had the FX6100 for around a year, and i liked it though it struggled in Crysis 3 and in Minecraft, i could run games...