Any secondary set will work, so try what you think you will enjoy.
Tankers received some changes recently, the most notable being an increase in the number of targets affected by AoEs.
For tanks i really like Fire Melee, Dark Melee and Staff Fighting, lots of AoE and utility in the case of DM and Staff.
Other sets i have tried and like for tanks is War Mace, Battle Axe, Electric Melee and Radiation Melee.
For pure Damage i like Super Strength, Energy Melee (recently improved), and stone Melee.
All of the other sets i have not tried as a tanker, and i'm sure others can give you better advice, but i say Try Them All.
After all that is what this game is about 🙂