My favorite, *endless* time over many, many months spent on her, tweaking every little detail and effing around with texture maps and nodes and stuff. Still, even the best likenesses are never truly done. I will always continue to tweak and tweak and tweak until she's perfect from every possible angle. Expressions are ultimately what kills you. You may have the neutral face flawless, but as soon as you dial up some smile, it's all trashed. Sometimes just moving a light will ruin a likeness too. That's the MOST frustrating aspect of this sort of endeavor.