As an employee of an association of meeting planners, we use five simple questions with a simple six-point Likert scale on levels of agreement for each question: Satisfaction with content, presenter, learned new knowledge and skills, etc.. And always an open-ended so they can leave feedback. We get complaints if we don't allow for written comments. We have also moved our surveys to a conference app, which gives us many more responses right after each session while it is fresh on attendees' minds.