|"Nvidia GT 610 2 GB and AMD Radeon HD 6670"|
"AMD has about 460 cores against 96 of nvidia"
AMD calls them Stream Processors, NVidia calls them CUDA cores. To do a reasonable comparison, either multiply the NVidia number by 5 or divide AMD number by 5. However, your numbers appear to be incorrect, they should be 480 for the HD 6670 vs 48 for the GT 610. 480/5 = 96 or 48 x 5 = 240, so the comparison is either 480 vs 240 or 96 vs 48. In other words, the HD 6670 should have roughly twice the processing power.
Memory is another issue. Is it 64-bit or 128-bit? GDDR3/DDR3 or GDDR5/DDR5? If good gaming performance is what you're after, 128-bit GDDR5 would be best, 128-bit GDDR3 is next, 64-bit cards shouldn't even be considered for gaming.
The Radeon HD 6670 is better than the GT 610, but either card is better than an onboard GPU.