charge off settlement

It's always best to start low (around 20%), as they will start high. And then go from there.
The % on credit cards depends on the account itself, some may go as low as 20%, some may not take less than 70%.

is it best to settle with the credit card co or the collection agency after an account has been charged off?

That depends on the collection agency, and even more - on the person actually handling the account. Many people on this board have reported that they had to wait for the original creditor to recall the debt before they could settle because the CA wouldn't budge. Some of them are highly uncooperative.
And the other way happens too. Some creditors are not willing to bend much and you have to wait for it to go to collections before you can negotiate.

Many hospitals have programs for people who cannot afford to pay. They do not advertise them. Call the hospitals billing department and ask if they have such a program in place. If not there may be an agency that they know of that can help. This is first hand knowledge. I owe about 2000 to Morton Plant here in Florida. My wife called the hospital and found out, because I am on unemployment, if I fill out a hardship form I can get the bills taken care of even though they are in the hands of a collector. The drug company, Squibb to be exact is also covering my meds! I will post this tomorrow for all to read but iI see Chrys is here so it must be time for me to go to bed,