"If you are single you always claim S-0."

I have many single clients who make decent money and own homes with mortgages, & property taxes, and are charitably inclined.  If they claim "single & zero" they would be substantially over-withheld and would have effectively made an interest-free loan to the government.  That's poor money management, and a disservice to the client.  

Blanket positions/statements are always (well, often? sometimes? generally?) not a good idea nor are they helpful.   Every situation may be different.

@rcooley25  TaxTools by CFS has a W-4 calculator that is very good.  You can download the software as a demo to play with & see if you like it.