Are you an American citizen or a legal resident? Are your co-founders as well? If both answers are yes, go with S-corp instead of C-corp initially. Why? Well, it allows you easier filing, pass-through taxation (you won't get taxed twice like with C-corp) and best of all, you can easily convert S-corp into C-corp by filing a single form (if you ever raise VC funding).

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.