On a personal note, I liked the Cochin airport better than the one in Trivandrum. I stayed at a place about the same distance from both, so that wasn't a factor. I felt that the people at the Cochin airport were quite a bit friendlier and more helpful, and the airport seemed cleaner and easier to navigate. Like the person above said, your first consideration should be your itinerary. Travel on roads can be a bit rough in India, especially if you have no prior experience with it.