I wouldn't think too highly of someone who always claimed a prize seat. There are exceptions, of course, such as when a medical condition makes it necessary.
This thread reminds me of someone I used to know. No matter what the situation, she'd lay claim to the best chair, the best bedroom (sharing lodging), and always very loudly. You could see people looking at her with incredulous expressions that seemed to say, "This is an adult?!"
I defer to older people, or people with disabilities. At the moment, I'm temporarily disabled (fractured ankle), in a cast, and walking with a cane. In the past I had no problem with sitting on the floor, but I can't do that right now. I'd not demand a good seat, but I'd be quite put out if I was left with only the floor to sit on. In my case, I'd politely ask if I could please have a seat, that the floor wouldn't work.