Of those four the Cube has the best fork (Reba). Cannondale and Trek have the Recon and the Focus has the 29er version of the Dart...neither of those forks are really that great. If I had to select between those four I'd lean towards the Cube for that reason alone plus it also seems to have better drivetrain components.
Also check out this one: http://www.airbornebicycles.com/products/97-goblin.aspx
One of the better deals out there if you can get shipping for a resonable amount. The reviews on this bike are really good and you simply can't beat that component mix for the price.