I certainly think that both bands have had good and bad songs over the years, but I think that out of the two, I'd have to say that Keane is my favorite. I've thoroughly enjoyed most of Hopes and Fears, and liked quite a few songs from Under the Iron Sea. Perfect Symmetry was certainly a change in sound for them, but it wasn't one that I disliked. I found a good number of them to be fun to listen to. Their EP, Night Train, left quite a bit to be desired, but when I listened to Strangeland, I found myself loving a majority of the songs.
As far as Coldplay is concerned, they've been hit or miss for me. I loved Strawberry Swing, Hurts Like Heaven (only with the intro song "Mylo Xyloto" though, because it does a good job of leading into it), In My Place, Life in Technicolor ii, Viva La Vida, The Scientist, Clocks, and Charlie Brown (definitely one of my favorites). Otherwise, they've had songs that I've tolerated, but not been very excited about. They certainly weren't songs that I would go out of my way to put onto playlists or listen to individually.