Both can be healthy and each provides valuable nutrients. Salmon provides fatty acids, so it is probably more healthy than steak if each is grown in a healthy, natural environment.

Each has the potential to be unhealthy. If the animal the steak is from has been raised in an unhealthy environment, and has been given steroids and antibiotics due to lack of exercise and possible disease, the steak will be unhealthy. If the salmon has been genetically modified (which is being done), the potential health effects are not known, but some propose that genetically modified foods are unhealthy.

So, which is healthier depends on many factors. Overall, natural salmon is probably healthier than steak.