I wear glasses 100% of the time because I don't do well with contacts. I have "dry eyes" and am constantly blinking funny or putting drops in my eyes with contacts. Any wind in my eyes and they dry out very quickly, so I know I can't wear them cycling, even with sunglasses. The breeze always comes around the frames and dries me out.

That being said, if you can wear contacts, that's the way I would go.