Which piece of equipment is more beneficial?

Treadmill.

Elliptical is good because its so easy on the joints however treadmill is better because it requires more energy, which will burn more calories.

In terms of heart health, both are cardio exercises so are about the same depending how hard you push yourself.

The most important thing is to do what you enjoy. If you hate the treadmill, don't push yourself to do it because you will end up giving up.

It's also good to mix up your exercise routing so incorporating both machines is a good idea, along with the bike and rower etc as well.

For me its the treadmill and I really prefer treadmill over an elliptical because treadmill is the best way to remain fit as you can walk on it and you can jog on it and those are the two major things to keep your heart healthy as well as the weight.

Down to a matter of personal opinion.

If you want to get better at running, lose weight and be healthy. Use the treadmill.

If you want to lose weight and be healthy but don't enjoy running. Use the elliptical.

Both will help you to lose weight and keep healthy when accompanied with a healthy diet.

The personal trainer where I go said the elliptical because it works more body parts ( arms as well as legs)

Treadmill is best.