With version 0.23, the antennas were rebalanced. But the stats listed on the construction screen seem to be misleading, because they have little relation to their actual performance. 

As an experiment I tested transmitting the atmospheric analysis experiment with each antenna and measured the energy and time (without unfolding animation) it required.

    Antenna     | Mass | Energy | Time
    ------------+------+--------+-----
    16          | .005 | 1000   | 45s
    DTS-M1      | .03  | 1500   | 30s
    88-88       | .025 | 2000   | 15s

As you can see, the antennas later in the tech tree have a higher transmission speed, but at the expense of a lower energy efficiency. But often the limiting factor when transmitting is energy supply, not transmission speed. To really make use of the faster antennas you need a lot more battery capacity and/or a lot more energy sources which means more mass to carry. 

That means when timing is not a concern, the first antenna, **the Communotron 16 is usually the optimal choice**. It has the lowest mass and needs fewer additional mass in form of batteries and solar panels to operate fluently. That means it is the most economic method to transmit your research results.

The only case where it might make sense to choose a faster antenna could be a probe which is planned to research the lower atmosphere of a planet but isn't equipped in any way to slow its descent and thus only has a limited time before it <strike>crashes onto the surface</strike> performs a lithobrake maneuver. By the way: When you equip your craft with multiple antennas you can transmit multiple results in parallel which saves you a lot of time.