He didn't specifically say "Phenom II x6".
OP, you need to tell us what models of which you are comparing. The phenom II ranges in core and speed configuration from $100-300 while the i7 ranges in cores and speed from $280-1000.
What model you compare from each depends on the uses for your computer.
So I recommend you give us a price range and the uses of your computer and we will suggest the best value in that price range as well as the best performance in that price range for your given uses.
As for functionality and reliability, all current CPUs are the same, featuring the same extension sets, which I assume you mean by functionality, and warranty (3 years).