if you are an scorp filing 1120S you only have to pay 15.3% social sec/medicare on the amount you actually pay yourself the rest of the net income will be subject to just the fed tax. just make sure you do pay yourself a resonable salary dont try and avoid all the employment tax.
if you are a sole proprietor you will have to pay self employment tax on all net income
also no liability shield with a sole proprietor
disidvantage is that extra tax return 1120s costs money to have prepared and some states have minimum tax that must be paid and annual filing fees
i do like the scorp because it is like having another person which has its own tax id number to build credit and borrow money almost like having another partner with which to do deals with.
Joe M