It depends on various factors. To list a few..
The individual's integrity - Sure, we all would love to have an extra $20,000 in our pockets, but at the expense of another individual? Individuals with no integrity would choose money over anything.
The needs of the individual - If you give a blank check to a billionaire, it's unlikely he would write a large number (unless he has no integrity). If you gave the same check to a poor man, the number might tend to be higher (but still depends on integrity)
What number would I choose? - Well that would depend on who gave it to me. If it was given to me by a rich friend with millions of dollars, and he gave it to me as a gift, I'd likely write down a fairly large number, and then ask him about it before cashing it in.