I do intend to pursue my idea, but I feel the connections and, more importantly, the full-time workload of doing it through YC would be very beneficial (there's a lot to be said for coding all day and then coming home to code all night...I think we can all agree that 8 hours of coding, especially if it isn't interesting, can be pretty draining). I've heard amazing things about the YC connections, and while I'm sure the company in question does have very good connections, I feel they probably pale in comparison to YC.

I will be working on the idea either way, but I am a strong believer in the idea that one is much more likely to succeed if there is the pressure of it being your primary focus and goal (I believe PG said this in an essay, though I don't recall which one), thus my need to decide between YC and moonlighting.