Ceres

Dwarf planet Ceres is the largest object in the asteroid belt between Mars and Jupiter, and it's the only dwarf planet located in the inner solar system. NASA spacecraft Dawn approached Ceres for its orbital mission in 2015. Dawn found Ceres's surface to be a mixture of water, ice, and hydrated minerals such as carbonates and clay. Ceres is one of the few places in our solar system where scientists would like to search for possible signs of life. Ceres has something a lot of other planets don't: water.

From an average distance of 413 million km., it takes sunlight 22 minutes to travel from the Sun to Ceres. Ceres takes 1,682 Earth days, or 4.6 Earth years, to make one trip around the Sun. As Ceres orbits the Sun, it completes one rotation every 9 hours, making its day length one of the shortest in the solar system. Ceres' axis of rotation is tilted just 4 degrees with respect to the plane of its orbit around the Sun. That means it spins nearly perfectly upright and doesn't experience seasons like other more tilted planets do.

Ceres is more similar to the terrestrial planets (Mercury, Venus, Earth, and Mars) than its asteroid neighbors, but it is much less dense. One of the similarities is a layered interior, but Ceres' layers aren’t as clearly defined. Ceres probably has a solid core and a mantle made of water ice. In fact, Ceres could be composed of as much as 25 percent water. If that is correct, Ceres has more water than Earth does. Ceres' crust is rocky and dusty with large salt deposits.

Ceres is covered in countless small, young craters. The lack of craters might be due to layers of ice just below the surface. Within some of Ceres' craters, there are regions that are always in shadow. It's possible that without direct sunlight, these "cold traps" could have water ice in them for long periods of time.

Ceres has a very thin atmosphere, and there is evidence it contains water vapor.

I guess this is enough information to justify a mission to Ceres compared to searching for water on Mars.