Which one is better for older adults with mobility restrictions: a walk-in tub or a walk-in shower?

My dad is not a patient person. We tried a walk-in tub, and he couldn’t deal with the fact that he needed to wait for the tub to become empty, and then he could open the door. It takes four or five seconds for the tub to become empty. My point is that it really depends on your beloved seniors which one they prefer.
My dad uses a wheelchair, and although a seat is included in the walk-in tub, it was tough for me to put him in the tub. I take him to the bathroom in a walk-in shower and just change his wheelchair, which is much easier than putting him in the tub. He agrees, too – true story. Also, the process of putting him in the tub was very hazardous. Everywhere was slippery, and it needed extra caution.