LEV covered most of the issues pretty well, I thought.
The biggest difference between becoming an S-Corp and not has to do with the "reasonable salary" and whether or not you want to pay into the Social Security system more than you need. Since that is easily 10.4% to 12.4% of your earnings, it can be substantial.
I can't tell you what a "reasonable salary" is, but I can tell you what an "unreasonable" one is. I say this, because if you don't want to pay into the SS more than necessary, then you might find 50K or 60K "reasonable" and minimize your SSA tax. You do that with the offset being that you cannot contribute as much to certain types of retirement plans.
A sole proprietor is not responsible for SUTA/FUTA, but this tax is usually pretty light ($56 FUTA per year, and state may be as low as a few hundred dollars) if you have a one-person payroll.
Your "three choices" have the following effect:
1. SMLLC no 2553 = taxed on Schedule C as a sole proprietor. Not subject to SUTA/FUTA, but ALL income subject to Social Security & Medicare taxes. Example: $200K earnings subject to all income tax and SS tax up to $110K and Medicare tax on all $200K.
2. SMLLC with S-Corp election = "Reasonable" wages must be paid, but you have some discretion as to how much is wages, and how much is your "profit distribution". Anything paid out as a profit distribution is NOT subject to SS OR Medicare taxes under current law. So if you pay out $60K in wages. Example: $60K wages subject to SS and Medicare. $135K net profit subject to NO Medicare or Social Security. Estimated SUTA/FUTA $200-400/year.
3. S-Corp instead of an LLC - NO TAX DIFFERENCE from #2, however you have more specific record-keeping, and legal requirements than an LLC electing to be taxed like an S-Corp.