Write them both a letter. Tell them that you're still very interested in attending because ______. It might be good to add something that's not in your application, but the idea of the letter is what is important. If it comes down to you and someone similar, the letter can put you over the top.
Whatever you do though... proof read. Have at least two other people read your letter before you send it out. If if comes down to someone with no letter and someone with a typo...
I had some success when I was applying by writing a letter. It didn't get me in to the school, but it got me on higher and higher waitlists until finally, a week after school started, a rejection (w/ invitation to apply as a transfer).