I have recently recorded you a video how to create two dropdowns saving their values in a user profile.
It is absolutely the same idea for a single dropdown.
I hope this information helps.
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Sitefinity CMS Ideas&Feedback Portal
and vote to affect the priority of the items