The "best" antenna depends strongly on the relative orientation of the transmitter and receiver. Since any RC craft is constantly and rapidly changing orientation, there is no antenna that will work well for the entire flight. A dipole, ground plane antenna, loop, or any other basic antenna will all perform about the same.
There are two reasons one antenna can not work in all orientations:
Firstly, a truly isotropic antenna can not exist. This means that any antenna you can build will have at least one null, a direction in which it does not radiate. When your craft is in the transmitter's null (or the transmitter is in the receiver's null), you may lose the signal.
Secondly, transverse waves such as EM radiation used in radio all have a polarization. When these polarizations are orthogonal, no power transfer occurs between transmitter and receiver. Again, signal is lost.
The solution is to have multiple antennas, in different orientations. This is called antenna diversity. If the receiver or transmitter have a number of antennas available, each in a different orientation, thus radiating in different directions, with different polarizations, then it's possible to select the one that is best at each instant.
Of course, this means your communications system has some way to determine what is "best". This can be done, for example, if periodically the transmitter sends a known synchronization sequence. The receiver can then analyze signals from each antenna, and using a method like regression analysis, calculate coefficients for each antenna that result in the best fit to the expected synchronization signal. The received signals from each antenna are then multiplied by these coefficients and added, and the result is used to recover the message. In the context of antenna arrays, this is called minimum mean square error weighting.
Modern wireless communications protocols, such as 802.11n or LTE Advanced do this. Usually it goes by the name of MIMO, which is, in essence, what I described. MIMO also includes some more advanced techniques like spatial multiplexing for increased data rate.
Unfortunately, no commodity RC system does this to my knowledge. As such you may be left to implement it yourself.