One of the sturdiest, funnest tanks I have ever made was Rad/Dark. Capped resists to S/L/E/F/T without Meltdown. With Meltdown add capped Negative, Cold at 83 and Psy at 72. Softcapped Melee, 36 to S/L/F/C, 20ish to everything else. And then add perma 1000 point absorb shield, 2 heals that do damage, endless endurance, tons of tohit debuffs, and excellent ST and AoE damage, capable of almost self capping damage for a few seconds with Meltdown and saturated Soul Drain with a Gaussian's Proc.