Dear …
Thank you for your proposal dated __(date)__ for our __(name of project/campaign)__. We were fortunate to have received some very impressive proposals for this project which made it difficult for us to choose a company that offered the best solutions to our needs.
After lengthy consideration, we have decided to go with __(name of company)__ for this project. We believe that they are offering the best combination of solutions in meeting our needs, pricing and time schedules.
Thank you for taking the time to prepare such a detailed and noteworthy proposal. We appreciate your effort and invite you to tender a proposal on our future projects.
Sincerely,