My advice is to incorporate in the state where you reside and work. In your case that would be MA, or possibly IL.
Interstate commerce laws haven't yet caught up to the internet age, and as a result there is little taxation involved with online businesses. Some exceptions may be:
If you incorporate in a state other than the state where your company has a physical presence, you will still have to register your company as a foreign entity in the state where you do have a physical presence. This means that you will have to pay yearly incorporation taxes in two states instead of one. Depending on your business, registering as a foreign entity in your home state (in addition to registering in another tax friendlier state) may wipe out any tax benefits you may get from another state. IMHO, this isn't usually worth it for startups. You can always do this later on when your business takes off.
This other question may also help you.