Rebuilding my credit?

I owe on 2 credit cards and 1 other bill (Dell computer) none of the three has been pain on in close to a year. i am about to get a loan through a co-signer to pay all these off. Would it better to pay them off in one chunk or pay them off a few payments at a time? which will rebuild my credit the best? Also is there a way to pay less than what the say u owe to pay it off? kinda like work a deal?