Which product, foam or pink batting would provide the best insulating factors in a 2x4 wall in a 90 year old house?

Spray in 'foam' is by far the best as it also seals any openings that would otherwise allow cold/hot air to enter. However, it is also more costly so you will have to consider the pros & cons. Be cheaper to place 'house wrap on the exterior to stop air leaks & use standard insulation batts. Let us know.

One more thing you should know about foam: Some types of foam insulation will exert pressure on your walls when it expands and can possibly bulge or bow the surface of the walls.