There is an entire two semester course in law school (usually called Business Organizations I & II) that addresses, pretty much exclusively, the question you ask. There are HUGE tax, securities, liability, governance, venture capital and dispute resolution implications to your choices. Once again, each of these legal issues has at least one course in law school. The point: you need a business attorney to help you with this question.
There are any number of excellent websites what spell out the difference between an ordinary partnership (no limitation on liability for partners), a Limited Liability Company, an ordinary Corporation (inc or corp are used to denote this entity) and an "S" Corporation (an ordinary corp which, by filing certain papers, is pretty much treated as a partnership for tax purposes). You still should hire a lawyer but you can do your "homework" and get the basics down so your not paying $250/hr to learn the differences between these entities.
Since it will be an online business, intellectual property (IP) will be much more important to you than other businesses so make sure the attorney can help you out with that too. For example, you want to make sure you can get the business name both as "Business Name" and as "BusinessName.com" (and, if possible, .net, .org, .biz, etc. too).
As a final thought, it usually costs, at least, 5 to 10 times as much money "to fix" choice of entity errors made while trying to save money while the business was new. Some are "unfixable." In case I have not made it clear, you need a face to face consultation so the above is just a general comment and not legal advice -- that can only be done after a lawyer learns your business model, future plans, etc. Good luck with your new business.
