If Credit Card Companies Sue You During Debt Settlement

Debt Settlement?
I've been in a credit counselling service for one year now and I am saving money on the side.
I've been recently offered a settelment on a sizeable debt I have. It's 60% what I owe the company but it's through a collection agency.
I know that by taking the settlement, the balance will go on my income at tax time, but I figure that the taxes I'll pay on it will be a lot less than what I would pay if I continue with the payment plan I have been using.
Are there any negatives to taking such a settlement? Can I ask that they consider that I paid it in full on my credit report?
If I can manage the three payments, why shouldn't I take the offer?
Sorry, I meant 60% OFF what I owe!!
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