If can buy a house that is listed for $100 for a 6% discount then the seller nets $94.
If I pay $100 for the house and the seller gives me a 6% credit then the seller nets $94.
The effect on the seller is the same under either scenario. The question is: what difference does each scenario make to you?
If you pay less, you need a smaller loan, your payments will be less and you overall interest cost will be less. If you pay more, but get the credit, your loan will be larger, your monthly payments will be larger and your overall interest cost will be higher. Both scenarios assume the same percentage of down payment vs. purchase price.
If you can afford the closing cost, paying a lower price seems like a better way to go. If you are struggling to come up with the cash for the closing costs, maybe the credit is best for you. Also, after the close, you may need additional cash for repairs, new flooring, new paint, appliances, and furniture. Maybe having the seller pay your closing costs allows you to save your cash for other things.