Choosing Ants as the next challenge is a bit of a bet. I'm a bit afraid that the game is too random to get really interesting AIs. Fog of war + food spawning at random places can bring early advantage to those players that explored the map 'just right'.

Disclaimer: I really enjoyed playing the Tron and PlanetWars challenges. Although I was a bit disappointed with my final ranking in PlanetWars (~80), I think that game was close to perfect.