My advice would be to start with the ninth doctor, as his first episode is the first of the "reboot" series. Start from "Rose" and work your way forward. It may take a while to get into that way but if you don't want to miss any important plot points I would start from there. If you don't have the time or patience to watch all six-and-a-half seasons that way (believe me it would take a while), then you could start with a few standalone episodes, like "Blink" and "Midnight". It really depends on how much time you have and how deep you want to get into it.