Ask HN: Should Startups Form as an LLC or C-Corp?

My "company" (which is currently not legally formed) is ready to begin sales, however I don't know what form of legal entity I should form.

I will eventually need outside investment, and definitely would like some liability protections. This leads me to consider a C-Corp (which would help with outside investment).

However, is it easier to just start with an LLC and just later convert to a C-Corp, or is it easier to start as a C-Corp?

Also, I was considering applying to Y Combinator, so do they have a preference?