As some have suggested, unless you are going to see actual investors (as distinct from lenders with convertible notes) any time soon, then starting with an LLC makes the most sense. It is easier to form and manage, and cheaper. As far as conversion, that depends on the state. For example, Washington State recently make it very easy and inexpensive to make the conversion. So, most likely, if you are not getting investors soon, the LLC is the best choice short term.
As an aside, you will hear lots of comments that you have to be a DE corporation. Just so you know, there is really no true justification for that perspective other than the typical lawyer approach to things of "this is just how it is done." It is the same reason lawyers always write dollar amounts as "four hundred twenty eight dollars and no cents ($428.00)." There is absolutely no need or reason to do that other than "that is how we have always written number since some obscure case 150 years ago."