So. You have a new logo and you want to protect it with a federal trademark registration. Should you register the words in the logo? The design? Both? A trademark registration on words covers the use of those words regardless of the font, size, color or configuration of the words. So why then would you not just register the words?
Registration of a logo protects you against someone using your logo with different words, or with no words at all. If your logo does not contain any words, or if your logo contains generic or descriptive (and therefore unprotectable) words, you have no choice but to register the logo.
If your words are unique and your logo is adaptable for use with other words (or no words), you should probably register both the words and the logo. On the other hand, if it would be very difficult for someone to use your logo without your words, or if your logo is generic i.e. (white block letters) your registration of the words alone may give you sufficient protection.
If you have any additional questions about logos or trademarks, contact your friendly neighborhood trademark lawyer who is probably dying share with someone the esoterica of trademark law.