It's more the level of componentry on the bike than anything.
The Cube and the other Kona have great frames and low grade components. The Fire Mountain is more rounded with a great frame and good components. Again, you wouldn't be disappointed with any of them.
The Fire Mountain would be lighter and the components would be more robust and perform better than their cheaper counterparts.
If you don't want or can't stretch, then don't worry. It's not a massive job to upgrade when bits break.