if you get the Phenom II x4 get this motherboard with it.
GIGABYTE GA-890GPA-UD3H AM3 AMD 890GX
if you get the i5-750 get this motherboard with it.
The i5 will preform better, however it will be more expensive.
if you are looking for price/preformance get the AMD Phenom II 955 BE (this is what i recommend, because this can be overclocked to at the very least match, but it can be pushed quite high)