There are hundreds of different styles of trainers, I find teenage lads seem to favour these huge Nike Air type, I wouldn't personally wear them. But to answer your question, trainers are comfortable if I'm walking about all day.
Not sure I would wear shoes with shorts in the summer.
For work it's boots or trainers depends on what I'm doing.
I wear trainers when I'm not working, but wear boots when the weather is bad or if I go walking.
Very rarely wear shoes.