From MESSENGER Finds New Evidence for Water Ice at Mercury's Poles :
Credits: NASA/John Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/National Astronomy and Ionosphere Center, Arecibo Observatory
Shown in red (in the image above) are areas of Mercury's north polar region that are in shadow in all images acquired by MESSENGER to date. The polar deposits imaged by Earth-based radar are in yellow.
New observations by the MESSENGER spacecraft provide compelling support for the long-held hypothesis that Mercury harbors abundant water ice and other frozen volatile materials in its permanently shadowed craters.
Three independent lines of evidence support this conclusion: the first measurements of excess hydrogen at Mercury's north pole with MESSENGER's Neutron Spectrometer, the first measurements of the reflectance of Mercury's polar deposits at near-infrared wavelengths with the Mercury Laser Altimeter (MLA), and the first detailed models of the surface and near-surface temperatures of Mercury's north polar regions that utilize the actual topography of Mercury's surface measured by the MLA. These findings are presented in three papers published online today in Science Express.
(Emphases by me)
For obvious reasons these findings of abundant water ice and other frozen volatile materials make the poles of Mercury much more suitable to compare with Mars in general with regard to colonization.
The most striking advantage for Mercury is of course that it gets much more energy from the Sun than Mars does:
about 12 times as much energy on average
Because the axial tilt of Mercury is only about 2 arc min., there is an elevated region near the north pole where that energy could be harvested all day and year around !
Furthermore Mercury has about the same surface gravity as Mars does, and it has a magnetic field that is strong enough to deflect the solar wind around the planet.
There's only one severe disadvantage that I could think of: the delta-v required for Mercury to enter Hohmann orbit is 7.5 km/s against 2.9 km/s for Mars, but that could be reduced with many flyby's like BepiColombo will attempt to do, so that will need much scheduling ahead !