With me it was the Original Trilogy for sure. The sheer power he radiated as well as his awesome voice and suit were likely the main draws for me. I definitely prefer Lord Vader(ie: suited Vader) to Vaderkin as I think that the latter lacks the regal and in someways even honorable aspects of Vader in the Original Trilogy. I still think my favorite Vader moment is when Luke walks into the Carbon Freezing Chamber and we see Vader's silhouette standing there completely still with his breathing echoing throughout the chamber. There's also the great lines throughout the duel such as "Impressive, most impressive, but you are not a Jedi yet." and "Your destiny lies with me, Skywalker."