There are different opinions about this topic. The goal is to heal and we heal by getting blood flow to carry nutrients to the injury and then have the blood carry waste or debris away from the injury.. With that understanding HEAT or ICE will both do that, by increasing blood flow. However the results will be different in regard to pain and mobility. So here are the differences.

Heat: When an injured area is heated, this opens the blood vessels to bring more blood to the area. With that there will be injured vessels that "leak" blood into the tissues, this is called "inflammation". Inflammation is not all bad because it serves as a splint or brace to stabilize the area and reduce range of motion that could re-injure the area. Additionally the inflammation will lead to an increase in sensitivity or discomfort with movement, this can be used to keep someone from re-injuring the area. 

  Ice: When an injury is iced the goal is tissue numbness.The increased blood flow comes when ice is removed. This increased blood flow is via constricted or narrowed vessels thus reducing the "leaking" of blood into surrounding tissue and therefore reduced inflammation. This allows for more mobility and decreased discomfort. The effects of icing is more comfortable, but also may increase vulnerability to re-injury if pain is the only factor in activity level.

Personally I prefer ice and the reduced discomfort, but an explanation and understanding of what is happening inside the body is vital with either process.

Dr. Ken