Which position is best? (answer is below)
As for workplace posture, the vast majority of my patients spend time in front of a computer, sometimes their entire workday. If their poor posture habits are made even worse due to an improper ergonomic setup, neck and back pain, headaches, etc., will eventually result. Following are several suggestions regarding workplace posture to minimize back and neck strain on the job.

Computer position – The monitor needs to be set so that the user does not have to look up or down to view it. Setting the screen so the top of it is at eye level is recommended. (Laptops obviously present a problem here. They should be positioned, wherever possible, so that the user’s head and neck are held in forward flexion to the least degree possible.)

Chair position – The seat should be at the proper height so that one’s feet can rest comfortably on the floor. If someone has short legs, placing something under their workstation to rest their feet on is incorrect workplace posture from a chair too low or desk too high recommended. (Working with one’s feet dangling above the floor will eventually result in pain.) The chair should have adequate back support and armrests. If the only support for the upper extremities being provided is a wrist rest, upper back and shoulder pain will develop much more quickly.

Phone – Holding the phone receiver between an ear and shoulder while using both hands on a keyboard puts considerable stress on the neck. I encourage all my patients that are doing this to get a headset, if possible, especially if they spend most of their day on the phone while at the computer. (A speaker phone is another option, but it obviously does not provide the level of privacy one has with a headset.)

Document Position – Looking back and forth all day long between paperwork lying flat on a desk and a computer screen is another habit which hastens the onset of muscle fatigue and pain. I recommend some type of document holder that allows paperwork to be positioned upright beside one’s monitor, so that the bulk of movement between it and the computer screen occurs with the eyes, not the head and neck. (For a few dollars on Amazon, you can have a document holder and headset by next week)

Of course! The first picture demonstrates the best posture.
By taking a few small steps to improve workplace posture, you can spare yourself from the postural stresses that result in headaches and spine pain.