It all depends on the game
I really enjoy the free lite versions as long as I don't get only a demo version. I love developers that only disable a few options that you don't miss when you start playing.
Free: if it only took you 2 afternoons of your time make it free (without ads)
If your game will be played like every day for the next weeks (Farmville, Bejeweled) free+ads will probably make you more money.