I love quilting retreats and go to as many as I can afford, but don't have one favorite. I've never been to a structured retreat, like those in the Elm Creek books, just the "do your own thang" type.
I take a number of projects, new and in-progress, in case I get finished, hung up, or just bored with something. It helps to have read through a pattern and have all the cutting done ahead of time, so I can get more done at the actual retreat.
Besides working on quilt projects, I've also started taking fabric to make at least one pair of pillowcases at each retreat, then I'll have a new set for me or one of my daughters. A friend, who is a nurse, makes herself a new scrub top or two at each retreat. It's a good way to get some little things done.