I personally believe that Burt Rutan's
White Knight/SpaceShipOne program is by far the leading contender to win the X-Prize, mostly because Rutan's company has demonstrated pretty much everything works. I actually see the first powered attempt to reach 100 km altitude on December 3, 2003 and the second attempt before December 17, 2003, the 100th Anniversary of the Wright Brothers' first successful powered flight.
Armadillo Aerospace's ideas seem intriguing but they've yet to build actual flyable hardware--let alone do anything close to a full-scale test flight!
Rutan is probably about 9 months ahead of Carmack in gettting something into space. The great thing about it is that Carmack will probably have his spacecraft flying into space in about a year. There will be competition and that's a great thing to have in this new space race.
Some other good news just appearing at space.com is that Rutan and Carmack have FAA approval for their flights. This was one of the big potential showstoppers, but it looks like the way is clear for Rutan's attempt in December and Carmack's attempt next year.
Two X Prize Teams Poised for Manned Spaceflight