No VC will ever invest into LLC and converting LLC to a C-corp is a pretty involved (and expensive) process.
If you're a foreign national or have a foreign national as a co-founder, you should go with C-corp.
You need to be a C-corp to raise money from a venture capitalist.
Do it in Delaware or make sure your home state doesn't have an enormous franchise fee.
From a tax perspective, the IRS doesn't recognize the LLC as a business entity type. If you own a single-member LLC you'll be taxed as a sole-proprietor by the IRS & pay income and self-employment taxes on the net taxable income of your LLC. If your LLC has more than one member you'll be taxed as a partnership. An LLC can elect to be taxed as a corporation, either C or S.
An advantage of the S Corp is the losses will flow to your personal return. This is likely to be most beneficial in the earlier years when you're pumping money into the company. As long as you have sufficient basis in the company, the losses are deducted from your ordinary income on your personal tax return.
The taxation of LLCs vary by state too. Some states have a low franchise tax on LLCs. CA, on the other hand, has a $800 minimum tax on LLC (and corporations). The franchise tax in some states is based on gross revenues so be aware of that if you expect to have low-margin product.
Take a look at http://www.biztaxtalk.com for more on taxation of various entity types.
However, most VCs won't fund an LLC for a number of legal reasons. If your LLC is planning to pitch to VCs, I'd recommend incorporating (into a C-corporation) before doing so. Sure, it will cost you a few thousand dollars in legal fees and paper work, but I don't know of any VCs that don't require incorporation first.
Also, I'd recommend incorporating in Delaware, since Delaware law is extremely forgiving to new startups. There's a reason why so many businesses are registered in that state...although, many startups have been incorporating in California recently as well.