I would personally recommend the 7850 because it is a bit faster and the bigger memory bus will help running AA.
They are both good though.
sir, the core speed of 650ti boost is 993mhz and 860mhz in 7850
the memory speed of 650ti boost is 1502mhz and 1200mhz in 7850
the memory bus of 650ti boost is 192bit and 256bit in 7850
the actual shader performance of 650ti boost is 768 and 665.6 in 7850
these whole thing are bothering me, please help me to choose the right value of money....