I dislike the idea of starting in V101, mostly because it takes close to an hour to EXIT Vault 101, because I find the beginning of FO3 boring, and because starting in New Vegas is short, simple and to the point. Story-wise, if I were to play a character that STARTED in DC then moved to New Vegas, then starting in V101 makes sense. But what if I want to make a character that was born, raised and currently living in New Vegas? Then I'm forced to go through the entire long-as-hell FO3 tutorial crap just so I can travel to the Mojave.
Giving us the ability to choose which beginning we should take is the best option.
However, IIRC, and I MIGHT be wrong, doesn't FO3 offer more chargen options than NV? So, if you could make it so the facegen thing that pops up that allows you to choose your race, hair etc use the FO3 one, even in NV.