I like the cube. It's maybe a bit generic, though.
In the end, I don't think it matters if the logo represents what the project is about. It only matters that it's distinct and recognizable. Look at the GIMP and Blender logos. Few people could probably tell you what they mean, but they each provide great brand recognition for those projects.
I also really like the caliper logo, though maybe the color scheme isn't my favorite. That could grow on me, though. The caliper logo also has a steampunk feel which, frankly, fits FreeCAD...
Anyway, I don't care what the logo is, but this thread needs to continue for two reasons:
First, having someone willing to do a bunch of good logo designs (and iterate on feedback) for free is something I wouldn't pass up. Ever.
Second, there has been talk about FreeCAD finally being ready for production. What that means depends on who you ask, but there's no question, it's grown a lot just in the last couple of years. Given that there's been discussion about moving away from the "alpha versioning" (i.e., FreeCAD 0.18 may end up being FreeCAD 18), it seems like now is a perfect time to consider refreshing the logo. A refreshed logo gets attention and signals to those outside our community that something's happening - that we're worth another look.