Cursed Foundry gives you the least plunder of all T4L3 Buildings Based on stats Circle of Elemental should give you about 10% more plunder than a Cursed Foundry Based on stats and it's 5% bonus a titans lair should give you about 1.1% more plunder than a Circle or Elemental (11.1% more plunder than a Cursed Foundry)
Titans give the most plunder per hit. They also give u a 5% bonus on the plunder from ONLY that one building. Coes give slightly less plunder but an extra 2 attacks. For the most plunder build 2 coe and the rest titans
1) Titan Lair + 1) Cursed Foundry is - Fewer Troops - Lower Overall stats - Slightly less plunder than 2) CoE. Do not mix Attack & Defense buildings if you can help it.