"Neither.

Ice is more abundant. "

Fine, what about if you talking about CO2 and H2O in all phases (liquid, solid, and gas {you can disregard Plasma}).
Another related question is how much Oxygen is on Mars? Of this Oxygen how much is joined with Hydrogen and how much is joined with Carbon?
On the Moon surface 40% of the mass is Oxygen. I assume Mars is similar.
On the Moon there is an apparent lack of carbon. On Mars there is more carbon. On Venus you a deep ocean of hot dense CO2 gas.
Let's call the surface the first 5 miles below the ground and including the atmosphere, compare the surface composition of Carbon from Earth, Moon, Venus, and Mars.
Now the Moon it is safe to say seems to have far less carbon than the others- why? Is it because the solar wind brings O which than bonds with carbon and the CO2 "sputters" or simply leaves the Moon. What about in dark cold craters of the lunar pole- there is thought to be H2O ice, but what about CO2 ice? If there was only a low percentage of CO2 at lunar poles does that mean H2O is more likely to also remain on Mars.
Or another question since Hydrogen is the most abundance element and Plasmatic Hydrogen (ok, so I lied, don't disregard Plasma:) is extremely reactive (and to lesser degree so is H2). Solar Hydrogen in plasma state in extremely low density but over billions of years (but also over large are of a planet) somehow changes this balance on Mars back to favoring more H2O than CO2. Though perhaps, impactors would dwarf the affect of the Sun in terms of H20 and CO2- tons of this material "rains down" daily- and of this, some percentage of it will be CO2 and H2O.