I have played both the Challenger and the Joust.
The challenger's playfield tilts depending on what is hit on the playfield. Not a bad idea, but it is an EM and played very slow.
The Joust on the other hand shows up at the Rocky Mountain Pinball Showdown, and Lyons Classic Pinballs has one as well. It is really fun to play, with two people, with one person, it is fair. The whole head-to-head competition is really a lot of fun. If I could find one for a reasonable price I would pick it up, but they are rare and seem to go for much more than I am willing to spend on a system 7 pin.
Mike