In my opinion Halo is generally only good if you played the first 2. I don't think if you pick up the franchise now you will get as much out of it.
Don't get me wrong, it is a very fun game and even the 3rd one is good to play, but you certainly won't get the most out of it because you won't have had the foundation of the first two laid down.
I wouldn't rate RAGE that highly, if I were you I would rent RAGE not buy it.
Well Rage is much more refined than any of the games in the halo series. I would say Halo, but Reach is really really bad. So i'm gonna go with Rage simply for the superior singleplayer experience.