I watched these two movies in one day, no prizes for guessing which one I preferred! If you haven't worked it out yet the answer is of course "The Road". I've also read the novel, which is pretty amazing. In some ways it felt like the movie was just an adaption of the novel rather than being a stand alone movie, but the acting and the atmosphere was pretty incredible. It's not a happy movie but it is a damn good one and you should watch it!
In regard to "Knowing" it's watchable but it won't be in my top ten movies of the year or anything like that, mostly because I find Nicolas Cage a little annoying.