Well, I think you're mixing terms just a bit here. Having a trademark and a service mark confer more or less the exact same protections. The main difference between the two is that for a trademark, the 'use in commerce' required for protection to commence and continue is an actual placement of the mark on goods and packaging, while the 'use in commerce' for a service mark is the placement of the mark in connection with the business on materials other than goods and packaging. So, whether you have a trademark or a service mark depends primarily on how you're using the mark, and certainly one mark can be both a trademark and a service mark. Whether you have a trademark or a service mark, registering the mark will confer additional protections.
The only difference between the registered mark ® and a trademark ™ or service mark ℠ is the fact that the ® may be used on a registered trademark or registered service mark, and ™ or ℠ may be used on either registered or unregistered marks. Once your trademark or service mark is registered with the USPTO, you may use ® on your mark whether it's a registered trademark or a registered service mark. In practice, a 'registered mark' is simply a trademark, service mark, or other mark which has been registered, and is mainly used to distinguish from unregistered marks.
Or, put another way, here's a quote from the USPTO website:
Do federal regulations govern the use of the designations "TM" or "SM" or the ® symbol?
If you claim rights to use a mark, you may use the "TM" (trademark) or "SM" (service mark) designation to alert the public to your claim of ownership of the mark, regardless of whether you have filed an application with the United States Patent and Trademark Office (USPTO). However, you may only use the federal registration symbol "®" after the USPTO actually registers a mark, and not while an application is pending.