This is my personal opinion!
I don't think there is anything wrong with scripted prayers, as one method of prayer.
As Christianity is (according to most) above all, a relationship with Christ, then we ought to have relational conversations with Him. As such, many of our prayers ought to "come from the heart," to use your phrase.
However, it is clear that in other relationships, not all conversations are ad-lib. Parents will sing songs to their children, or recite poems. Friends quote topical movies or comedy sketches with each other. Lovers will recite poetry or sing songs to each other (probably far less often than most women would like).
These "recited" forms of conversation are not invalid, and can do a lot to deepen the relationship--for both parties involved.
I remember fondly a poem both of my parents used to recite to me when I was 3-4 years old. The fact that they didn't write the words, or that they used the same words repeatedly did not detract from the love they were communicating to me in those words. And in fact, the repetitiveness served to ingrain the poem in my mind for many years to come.
Now, if my parents only recited poems to me, I would consider that problematic. While it might be a meaningful form of communication, it's not a very flexible one.
Likewise, if our only, or perhaps even primary, method of communication with God is through recited words, I would consider that to be a problem.
Also, if when we recite words, it is simply acting out a formula, then it's not really communication. The recited words must have meaning that we understand and that we are attempting to communicate to be meaningful.