A. I had visited them two months ago.
B. I visited them two months ago.
Which one is correct?
A. I had visited them two months ago.
B. I visited them two months ago.
Which one is correct?
"Which one is correct" cannot be answered without further context. However this information can help you decide for yourself.
A. is pluperfect. B. is present perfect. So, A. is further back in time than some other event.
And in general: http://en.wikipedia.org/wiki/Perfect_(grammar)#English