I hold doors for anyone that is close to the door, I consider it a kind gesture. Better than letting the door slam in their faces haha.
I hold the door for the person behind me, or a group I am with. It's just polite to do so. Also body language is 70% of all human communication. Being last in the door shows control of the situation and confidence in one's status.
I will open the door for everyone. I just hate the alpha males who refuse to let another man open the door for them.