Q:

Coplanar waveguide vs open space?

I'm routing a U.FL connector to a cellular module (Telit GE864).
According to this calculator a 1mm track with 0.16mm gaps should provide a 52Ω impedance path to an U.FL antenna connector.
A Sparkfun breakout board for a similar module uses an open space (~1 cm high) with a far wider trace (2.8mm). Both traces are approximately 6mm long.
Calculator:

Sparkfun: 

Which of these connections is preferable?

A:

Like the comments say, the Sparkfun layout is a microstrip layout. Microstrip is a waveguide where the return path is on the ground plane beneath the signal path. Whereas coplanar waveguide is a waveguide where the return path is (predominately) on copper regions in the same plane as (coplanar with) the signal conductor. 
I think your design is better than Sparkfun's.
The benefit of coplanar waveguide in this design is that it allows a narrower trace which matches the pad dimensions better and doesn't need a neck-down before readhing the antenna pad. 
In other situations, microstrip might be preferred because a wider trace will have lower resistive loss, or because it's impractical to maintain symmetric ground regions on both sides of the signal trace.

