What is the "best interests of the child" in a custody dispute?

In New Brunswick, the “best interests of the child[ren]” has been broken into sub-issues by Graser J. in the much quoted judgment in Rideout v. Rideout [1998] N.B.J. No. 233 (N.B.Q.B.) where he suggested the following matters guide the determination of what is in the child’s best interest. At paragraphs 36-7 he set them out saying in part: There are many other considerations which automatically flow in disputes over custody. They include: 1. Which parent offers the most stability as a family unit; 2. Which parent appears most prepared to communicate in a mature and responsible manner with the other parent; 3. Which parent is more able to set aside personal animosity and be generous with access arrangements; 4. Which parent shows promise of being an appropriate role model for the children, and exhibits a sense of values and directions; 5. Which parent is more prepared to broaden the scope of the child's life with learning, associations and challenges; 6. Which parent provides the best cushion for the child against the stresses of marriage breakdown; 7. Does one parent play mind games with the child and carelessly expose the child to domestic turmoil; 8. Where will the overall long term intellectual and security interests of the child best be served; 9. Will there be material provisions that meet at least minimal standards; 10. Which parent appears most prepared to give priority to the child's best interest over and above his own; 11. Which parent exhibits the most maturity and ability to accept and deal with responsibility; 12. Is there a positive or negative effect with respect to the involvement of third parties with either parent on the welfare of the child and is such effect financial or emotional; 13. Where is the long term best interests of the child served.