I would suggest going with metal. You can run into problems when pulling large amounts of cabling through PVC due to heat. If you choose steel, it will also assist in reducing and EMI.
Steel is more maleable than PVC which reduces the number of elbows you may need to introduce.
You could also use PVC for the runs and metal for the joints if you are looking for the most economical option.
Bottom line: I would go with metal.