Smelly homeless dudes is another matter. Longterm, as rail transit becomes faster and more prevalent, I expect to see more airport style passenger/passerby segregation--with facilities provided only for those who have purchased a ticket. You are only permitted on the platform for the Phoenix LRT if you have purchased a ticket, for example. This suggests the emergence of 'semi-public' spaces.
Basic public seating is durable and easily cleaned. For outdoor seating, this means metal or plastic. For indoor uses, this can include limited use of cloth. Bonus points for the ability to be repositioned, as well as the ability to be stacked. Alternately, heavy can be a virtue, as theft prevention. Padding ages poorly, and so must be minimal, making shape even more critical.
For volume seating, ledges and benches are difficult to beat, and can entail some personal space issues. (One of the reason airport seating is broken into attached chairs, I suspect.
I invite you to imagine what a 'public' lounge chair would look like. Google images provides some ideas.
|'Mesh' nature of chair evokes other outdoor seating.|
|Reclining and potentially stackable?|
|Nice shape, but swiveling capacity is unnecessary|
|Nice shape, but looks fragile|
|Very simple, but legs seem vulnerable|
|Strange, but structurally sound|
|Functional, but no arm support|
|No legs, but look very comfortable|