http://www.reddit.com/r/SWGalaxyOfHeroes/comments/4x7k48/minimum_requirements_to_3_t3_of_mod_challenges/
Nebit is generally best lead. This is an example of a team that cleared it:
Nebit (L) - 6s, lvl78, G8, 7/8/7/7, 3-5s Health mods
Jawa - 7s, lvl80, G9, 8/7/7, no mods (normally 1s potency set but I forgot)
Jawa Engineer - 7s, lvl80, G9, 8/8/7/7, 5s Arena Caliber Health Mods (208 speed)
Dathcha - 6s, lvl 70, G8, 5/6/7/3, no mods
Scavenger - 5s, lvl 51, G7, 5/5/5/4, no mods