which is better- quit claim or purchase?

My mother is interested in selling me her house, at a lower than market value price. Would it be better for her to issue a quit-claim deed, and me take out a loan for the agreed-upon amount to give her the money, or an outright purchase? My siblings are all aware of the potential sale to me, and the agreed-on price, but I don't want anyone coming back later to say they were "cheated" out of their inheritance. I am the primary caregiver for my mother, and we have agreed that she will remain in the house as long as physically possible for her to do so.