For most people the answer is probably self-wielding infinity. 200 fcr is my preferred style though. I usually use wizspike, but for max dps you can use eschuta and maybe even ormus. You must max warmth instead of energy shield, unless you want to pot like mad each game. 200 fcr only achieves enough mana sustain to not pot if your sorc is very high level with a near perfect inventory (20/17s, nice life skillers) or barb BO. 1 pt fire wall, 1 pt fire mastery, 1 pt thunderstorm, 1 pt energy shield.
If the -res charm crafts make their way into a future patch, the answer will be 200 and it won't even be close. But also, that'll open up doors for other builds like 200 fcr fireball/hydra that might even outpace 200 nova then, depending on zone/clear tactics (pack hunting vs full clearing).