Gusev Crater, Mars (credit: Spirit Rover, NASA)
NASA just just announced the landing spot finalists for the next Mars lander. According to NASA they include:
1. Gusev Crater where the Spirit rover found "mineral springs once burbled up from the rocks of the Columbia Hills and hot springs flowed. The rover's discovery was an especially welcome surprise because Spirit had not found signs of water anywhere else in the 100-mile wide crater. Studies of its older data records showed evidence that past floods that may have formed a shallow lake in Gusev".
Jezero Crater, Mars (credit: Mars Reconnaissance Orbiter, NASA
2. Jezero Crater where "on-again, off-again Martian wet periods were discovered. Water filled and drained away from the crater on at least two occasions and more than 3.5 billion years ago, river channels spilled over the crater wall to create a lake. Evidence shows that clay minerals flowed from the surrounding area into the crater after the lake dried up. Conceivably, microbial life could have lived in Jezero during one or more of these wet times. If so, signs of their remains might be found in lakebed sediments."
Syrtis Major, Mars (credit: Mars Science Lab, NASA, JPL-Caltech, and University of Arizona
3. Syrtis Major where "volcanic activity once warmed the are and underground heat sources made hot springs flow so that surface ice melted. Microbes could have flourished in liquid water that was in contact with minerals here. The layered terrain of NE Syrtis holds a rich record of the interactions that occurred between water and minerals over successive periods of early Mars history."
The final selection depends on the variety of rocks and "soils" at each site and which of those are from an ancient time when Mars could have supported life. The former multiple times for ponds and river deltas in Jezero Crater look very promising. The new Mars mission is scheduled to launch in 2020.