If I were starting from scratch right now, I would go with Fidelity given the 0 fee funds. Currently I have enough crap with Vanguard that the zero fee funds aren't enticing enough for me to move anything over.
The 0 fee funds are new enough that some folks are preaching caution, in that you don't know what the performance will be. Technically that is true, as they are tracking a new index and don't have any performance history. But past history isn't an indication of future performance anyway, so IMO the point is moot. Unless you think Fidelity is going to fuck it up somehow, their 0 fee funds will probably perform very similarly to VTSAX/VTIAX, and probably a tiny bit better due to the lack of fees. Just my opinion.
Especially if you have less that $10k lump sum to invest right now, I would tend toward Fidelity even more strongly. Under 10k and you will be paying investor share class fees at Vanguard. And under $3k and you can't get in to anything but target date funds. And under $1k, not even that. This is all for the index mutual funds. You could also go the ETF route at Vanguard, and invest starting at the cost of 1 share. So there's that. Again this comes down a little bit to preference. I like the simplicity of the mutual funds (e.g. no cash drag). YMMV.
Past the fee issue, it is a lot of personal preference. Some find the Fidelity website to be better than the Vanguard website. Personally I hate them both in different ways. Fidelity does have better support hours if you need to call them. This comes up rarely enough for me that I don't care.