Generally, a low horizontal dipole doesn't do a good job of radiating power to where you want it. I found an interesting analysis of horizontal dipole height, which ran a number of simulations and found that at low heights (less than 1 wavelength, roughly) the dipole's radiation pattern has a significant vertical lobe. At heights of 0.2 wavelengths or less off the ground, the direction of maximum gain is straight up.
I have read elsewhere that low dipoles also tend to radiate a lot of power into the ground. So, you would be spending a lot of your power heating the ground and space.
I believe polarization is important for groundwave propagation, but for skywave propagation it is minimally important unless you have a specific QRM issue that you need to work around. So, for the purposes of this answer, I will assume that polarization is not an important consideration.
With that in mind, a vertical dipole is likely to be more effective. In practice it's likely to be similar to a monopole with radials, which is an antenna configuration that is widely used with positive results.