When it comes to electricity use, the first antenna, the Communotron 16, is the most efficient one. It is also the one with the lowest mass by far.
But when it comes to speed, the Comms DTS-M1 will transmit your research results faster than any other antenna. There are, however, few situations where transmission speed is essential. Usually the limiting factor in sending large amounts of research data is the energy supply. One case where it might matter 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 crashes onto the surface 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.
The Communotron 88-88 is the one with the highest energy consumption per Mit while being in between the others in transmission speed and being only slightly lighter than the Comms DTS-M1. That means that it is usually a sub-par antenna which should be avoided. Its fold/unfold animation looks cool, though.
For most situations I would recommend the Communotron 16.
Source for antenna stats: http://wiki.kerbalspaceprogram.com/wiki/Antenna