Imagine you're back in high school, planning to ask out a fellow classmate to the prom. You approach your potential date, "Would you be interested in going with me to the dance? You're my second or third choice."
Not very compelling...The same is true for letters of intent: I've had several applicants ask me if it's okay to say that an institution is their "second or third choice" or "one of my top" picks.
That does not sound very flattering. Instead you can say something like "I would be thrilled to be at your institution," or " I’m confident I can make a positive contribution." In other words, you don't need to lie (which I never recommend); but you don't have to shoot yourself in the foot either.
I do edit letters of intent and have been busy with them this season. Let me know if you need assistance.