If you are flipping real estate, an S corp may be better than an LLC. Flipping income can easily be categorized by the IRS as “earned income” and thus subject to self employment tax through an LLC, particularly if it is single member. An S corp will shield part your income from this tax.
Always speak with an accountant to review the tax issues before choosing an entity to form, because most attorneys are not tax savvy.
This will depend upon whether you plan to only flip houses for short term investments, or do you also plan to buy and hold properties for long term and earn rental income from those investments. Flipping houses is generally treated as ordinary income, so you don't benefit from long term or short term capital gain treatment. If the LLC is a single member LLC and is disregarded for federal tax purposes, the ordinary income will be subject to ordinary federal income tax rates, as well as federal self-employment taxes. If the LLC makes an S corporation election, the pass through earnings are only subject to federal income taxes, however, as the sole shareholder that runs the business, you'll need to pay yourself a "reasonable" salary, so you will incur some payroll tax expense. The downside to holding real estate in an S corporation, is the asset can't be transferred or distributed out of the entity without creating a taxable event. Also, if the real estate purchases are financed through bank loans or third party debt, the shareholders are not able to add the liability balances to their basis in the stock, unlike an LLC taxed as a partnership, where a partner's total basis is the capital account plus their allocable share of the partnership liabilities. There are structures where you can create an LLC partnership where you own 99% of the LLC units while another S corporation owns 1% as the GP manager. You can pay a management fee from the LLC into the S corporation.