Question formats for donor surveys

For those who have conducted donor surveys – do you find it best to have choices/drop downs for certain questions, or do you go with all free-form text responses? E.g. “What other philanthropic areas do you support” – would you recommend checkbox options with an “other” option – or open text? As we are working on introducing more donor surveys to our communications and engagement strategies, I am tempted to go with more pre-loaded options in order to be able to capture cleaner data, but I am also concerned about limiting our donors’ ability to share authentic feedback.