I would strongly suggest starting with
The Eleventh Hour but... I'm not so sure when I think about it.
Imagine having
Victory of the Daleks instead of
Dalek as your introduction to the Daleks. I'm not sure I could put somebody through that. They'd then meet River Song and the Weeping Angels, not really understanding their significance. They'd also miss out on the Ninth Doctor, the best Doctor of the revived series.
Just start with Hartnell. His first season is better than any of the past 7.