I am not an attorney nor an accountant. This is not "professional advice".

An S-Corp is like a pipe you run water (revenue) through for tax benefits.

An LLC is a more rounded entity.

If you're planning to raise money, issue stock, or sell the firm, the LLC is the better choice.

My accountant recommended an S-Corp which has served me well for the past few years. But there will come a time when my revenue exceeds a certain level, and it will make sense to make the jump to an LLC.

These are two good articles on the topic:

http://www.feinberghanson.com/LLCvsSCorp.html

(very good on exit strategy discussion)

http://www.bizfilings.com/learn/s-corporation-advantages-and-disadvantages.aspx

(in-depth S-Corp discussion).

The S-Corp suits me well right now as a primarily service/consulting business where I usually work alone.

The type of structure will depend upon a number of factors, which include the type of business to be conducted, the tax residency of the owners, whether you need employees, fixed assets, etc. An S corporation election can provide favorable tax treatment with respect to self employment taxes, however, the operating structure is much more stringent than a traditional LLC that is taxed as a single member LLC or a partnership. S corporations are only permitted to issue one class of stock, provide no tax basis in entity level liabilities, no step up in S corporation asset basis at death of the shareholder, among other considerations. Whether you decide to use an LLC, a corporation with an S election, or an LLC with an S corporation election, the decision should be made based upon your facts and circumstances, as well as your short and long term goals. I would recommend consulting with a tax adviser to discuss your various options.