Paper is the most common thing I choose. I tend to pick it if I playing against a guy. Males are more likely to pick rock. If I play against a girl I'd use rock. Girls are more likely to pick scissors. I do factor in their personality to the mix. Then I try and sense what they'll pick. The I put it together and make my decision. It only takes seconds to process this information.
Now I'll have to pick a new one >:3
If I do a rock I can punch you if I lose.