Hi newcomer and welcome to the Tom's hardware forum.
1- i3 is a 32nm the c2d is a 65nm and 45nm, the c2d needs more power and generate more heat. Win the i3
2- The i3 have integrated graphics, the c2d doesn't have it. Another point for the i3
3- The i3 have PCI-e 2.0 controller, couple of them comes with 2X8 along with da 1X16 support, the c2d doesn't have PCI-E controller. Again, win the i3
4- 2 channel integrated memory controller, again the c2d doesn't have this feature. Win the i3.
5- The i3 have hyper threading, the C2D doesn't have it. Win the i3.
6- The i3 is socket 1156 and the c2d is 775, win the i3 because is a newer socket