Memory is best. If I'm watching another performer singing from words on a music stand or crib sheet I always get the impression that I'm sitting watching them practice and I'd rather watch and listen to a performance of a song. If you get some words wrong, it's not crucial, much more important is your interpretaion of the number. We all hit wrong chords and get verses mixed up from time to time but what I want to see is a performance of a song not a paint by numbers tune. The other thing is once you start to rely on crib sheets it's very hard to move away from them. Those comfort zones are very hard to escape from. You can only practice live performance by doing it live, so start as you mean to go on. I've seen performers struggle at outdoor gigs when the wind has blown over their lyrics or poor lighting has left them unable to read or they can't start a number until they find the right page in their folder, which is on the floor underneath some guitar leads! It's really best to learn the song,get the feel of it and let it flow out. It also builds your confidence.It's your decision to go out and play live so I think you owe it to your audience, it also means you can look at them and not stare at a sheet of paper.