BOF,
My oxygen co, prefers E tanks because they're easy to transport, both in the truck and around your house. I keep a rack of 10 in my front hall closet. Then transfer 2 at a time to my "CH Chair". Then I put the empties in a rack on the front porch for the O2 guy to swap out whenever he comes around. You can easily carry an E tank, but the M and M60, not so easily.
J