Suggestions for declining a job offer

I feel incredibly fortunate that I received two great job offers. Both companies know I received another offer. I need to tell one company "no thanks"

Any suggestions of how to word my decline to build the relationship and keep the doors open for the furture?

Thank you.

How about something along the lines of...Thank you so much for taking the time to meet with me the past [time period]. I thoroughly enjoyed my conversations with the team and learning more about x, y and z. I have decided to accept another offer at this time, but I would love to keep chatting [/talk again] should future opportunities come up!
Thank you!